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DESCRIPTIVE MINERALOGY
MINERALOGY
BY
WILLIAM SHIRLEY BAYLEY, PH.D.
PBOFXBSOR OP GEOLOGY. T7NTVTBBSITY OF ILLINOIS
AUTHOR OF "BLEMENTABY CBYSTAI,IX)OKAPHX "
"WITH TWO HTCnSTDKED AND SIXTY-EIGHT ILLUSTRATIONS
D. APPLETON AND COMPANY
NEW YORK AND LONDON
1917
COPYRIGHT, 1917, BY
D APPLETON AND COMPANY
TO
MY HELPER
MY WIFE
THIS BOOK IS
DEDICATED
PREFACE
THE following pages are presented with the purpose of affording
students a comprehensive view of modern mineralogy rather than a
detailed knowledge of many minerals The -minerals selected for
description are not necessarily those that are most common nor those
that occur in greatest quantity The list includes those that are of
scientific interest or of economic importance, and, in addition, those
that illustrate some principle employed in the classification of minerals.
The volume is not a reference book. It is offered solely as a textbook
It does not pretend to furnish a complete discussion of the mineral
kingdom, nor a means of determining the nature of any mineral that
may be met with The chapters devoted to the processes of deter-
minative mineralogy are brief , and the familiar " key to the determina-
tion of species " is omitted In place of the latter is a simple guide
to the descriptions of minerals to be found in the body of the text.
For more complete determinative tables the reader is referred to one
of the many good books that are devoted entirely to this phase of the
subject. In the descriptions of the characteristic crystals of minerals
both the Naumann and the Miller systems of notation are employed,
the former because of its almost general use in the more important refer-
ence books and the latter because of its almost universal use in modern
crystallography investigations The student must be familiar with
both notations It is thought that this familiarity can be best acquired
by employing the two notations side by side
In preparing the descriptive matter the author has made extensive
use of Hintze's Handbuch der Mvrwralogie. The figures illustrating
crystal forms are taken from many sources. A few illustrations have
VII
viii PREFACE
been made especially for this volume. Figures copied to illustrate
special features are accredited to their authors. The statistics are
mainly from the Mineral Resources of the Umted States They are
given for the year 1912 because this was a more nearly normal year in
trade than any that has followed
The author is under obligation to the McGraw-Hill Book Company
for permission to reproduce a number of illustrations originally published
in his Elements of Crystallography, and also for the use of the original
engravings m making the plates for Figures n, 33, 71, 90, no, 114, 115,
118, 160, 191, 194, 224, 240, and 248.
W. S. BAYLEY.
CONTENTS
PART I
GENERAL CHEMICAL MINERALOGY
CHAPTER PAGE
I THE COMPOSITION AND CLASSIFICATION OF MINERALS i
II THE FORMATION OF MINERALS AND THEIR ALTERATIONS 17
i
PART II
DESCRIPTIVE MINERALOGY
III INTRODUCTION— THE ELEMENTS 36
IV THE SULPHIDES, TELLURIDES, SELENIDES, ARSENIDES, AND
ANTIMONIDES 68
V THE SULPHO-SALTS AND SULPHO-FERRITES. Il6
VI THE CHLORIDES, BROMIDES, IODIDES, AND FLUORIDES. 134
VII THE OXIDES 146
VIII THE HYDROXIDES 179
IX. THE ALUMINATES, FERRITES, CHROMITES AND MANGANTTES 195
X. THE NITRATES AND BORATES 205
XI THE CARBONATES 212
XII THE SULPHATES 236
XIH THE CHROMATES, TUNGSTATES AND MOLYBDATES 253
XIV THE PHOSPHATES, ARSENATES AND VANADATES. 261
XV THE COLUMBATES, TANTALATES AND URANATES 293
XVI THE SILICATES THE ANHYDROUS ORTHOSELICATES . 300
XVII THE SILICATES THE ANHYDROUS METASILICATES . 359
XVIII THE SILICATES THE ANHYDROUS TRIMETASILICATES. . 408
XIX THE SILICATES THE ANHYDROUS POLYSILICATES . 426
XX THE SILICATES THE HYDRATED SILICATES . 441
XXI THE SILICATES THE TITANATES AND TTTANOSILICATES. .. 461
PART III
DETERMINATIVE MINERALOGY
XXII GENERAL PRINCIPLES OF BLOWPIPE ANALYSIS. 467
XXIH CHARACTERISTIC REACTIONS OP THE MORE IMPORTANT ELEMENTS
AND Aero RADICALS, , . 483
ix
CONTENTS
APPENDICES
CHAPTER PAGE
I GUIDE TO THE DESCRIPTIONS or MINERALS 495
II LIST or THE MORE IMPORTANT MINER AIS ARRANGED ACCORD-
ING TO THEIR PRINCIPAL CoNSTrrui'Nib 515
III LIST OP MINERALS ARRANGED ACCORDING TO THEIR CRYS-
TALLIZATION 521
IV LIST OF REFERENCE BOOKS 527
INDEX 529
LIST OF ILLUSTRATIONS
FIGURE PAGE
1 Sodium fluosihcate crystals ... 14
2 Potassium fluosihcate crystals 14
3 Cross-section of symmetrical vein 21
4 Cross-section of vein in green porphyry 24
5 Dionte dike cutting granite gneiss 26
6 Vein in Griffith mine 27
7 Vein forming original ore-body, Butte, Mont 27
8 Druse of Smithsonite 28
9 Geodes containing calcite 29
10 Alteration of ohvine into serpentine 31
11 Etch figures in cubic face of diamond 38
12 Crystal of diamond with rounded edges and faces 38
13 Octahedron of diamond 38
14 Principal "cuts" of diamonds 42
15 Premier diamond mines m South Africa 43
1 6 The Cullman diamond 43
17 Gems cut from Culhnan diamond . 44
1 8 The Tiffany diamond 44
19 Sulphur crystals 47
20 Distorted crystal of sulphur. ... 47
21 Copper crystal 53
22 Crystal of copper from ELeweenaw Point 53
23 Plate of silver from Comagas Mine, Cobalt 57
24. Octahedral skeleton crystal of gold with etched faces 58
25 Iron meteonte 65
26 Widmanstatten figures on etched surface of meteonte 66
27 Realgar crystal . . 70
28 Stibrute crystal 72
29 Galena crystal 81
30 Galena crystals . 82
31 Chalcocite crystal 85
32 Complex chalcocite twin 85
33 Tetrahedral crystal of sphalerite 88
34. Sphalerite crystal , 88
35 Sphalerite octahedron . 88
36 Greenockite crystal . . 91
37 Pyrrhotite crystal. 92
xu LIST OF ILLUSTRATIONS
FIGURE PAGE
38 Cinnabar crystals 98
39 Group of pyrite crystals in which the cube predominates 102
40 Pyrite crystals on which 0(111) predominates 102
41 Pyrite crystal 102
42 Group of pyrite crystals 103
43 Pyrite mterpenetration twin 103
44 Marcasite crystal no
45 Marcasite crystal with forms as indicated m Fig 44 no
46 Twin of marcasite no
47 Spearhead group of marcasite no
48 Arsenopynte crystals 112
49 Crystal of pyrargyrite ng
50 Crystal of proustite 119
51 Bournonite crystal 121
52 Bournonite fourlmg twinned 121
53 Enargite crystal 123
54 Stephanite crystal 125
55 Tetrahednte crystal I28
56 Chalcopynte crystal I3I
57 Chalcopynte 131
58 Chalcopynte twin 13!
59 Hopper-shaped cube of halite , 135
60 Group of fluonte crystals from Weardale Co 139
6 1 Crystal of fluonte !4O
62 Interpenetration cubes of fluonte, twin- 140
63 Photographs of snow crystals 147
64 Zmcite crystal !^0
65 Hematite crystals j^
66 Corundum crystal j^
67 Corundum crystal ^5
68 Corundum crystal I^
69 Quartz crystal exhibiting rhombohedral symmetry 159
70 Ideal (A) and distorted (B) quartz crystals . 159
71 Etch figures on two quartz crystals of the same form , 160
72 Group of quartz crystals , jgo
73 Tapenng quartz crystal X5X
74 Quartz crystal , ufa
75 Supplementary twins of quartz. , ,162
76 Quartz twinned I0*3
77 Cassitente crystal , . . 169
78 Cassitente crystal , ^
79 Cassitente twinned j$g
80 Rutile crystals 172
81. Rutile eightluig twinned , . , 2
LIST OP ILLUSTRATIONS
FIGURE
82 Rutile twinned . . 172
83 Rutile cycbc sixling twinned j^
84 Rutile twinned ^.
85 Anatase crystal I77
86 Anatase crystal I77
87 Brookite crystals I73
88 Brucite crystal f !32
89 Limonite stalactites in Silverbow mine. . , 184
90 Botryoidal hmorute . . jg^
91 Pisohtic bauxite from near Rock Run . 187
92 Diaspore crystals , I9O
93 Mangamte crystal . . I92
94 Group of prismatic mangamte crystals 192
95 Mangamte crystal twinned . . 193
96 Spinel twin . . ig5
97 Spinel crystal . 196
98 Magnetite crystal . 198
99 Chrysoberyl crystal 203
100 Chrysoberyl twinned . . 203
101 Chrysoberyl pseudohexagonal sixling . 203
102 Hausmanmte . . 204
103. Borax crystal . . 207
104 Colemamte crystals .... 209
105 Boracite crystal 211
106 Calcite crystal . 214
107 Calcite crystals 214
108 Calcite crystals 214
109 Calcite . ....... 214
no Prismatic crystals of calcite 215
in Calcite . 215
112 Calcite twin and polysynthetic trilling. 215
113 Calcite 216
114 Artificial twin of calcite , 216
115 Thin section of marble viewed by polarized fight. . 216
1 16. Aragonite crystal 224
117. Aragonite twin 224
118 Tnlhng of aragomte 224
119 Withente twinned . 226
120. Cerussite crystal . . 227
121. Cerussite tnllmg twinned . , 227
122. Cerussite trilling twinned 227
123. Radiate groups of cerussite on galena . . -228
124. Dolomite crystal. . - 229
125. Group of dolomite crystals. . 230
X1V LIST OF ILLUSTRATIONS
FIGURE PAGE
126 Malachite crystal .232
127 Azurite crystals 233
128 Trona crystal 235
129 Gayhissite crystal 235
130 Glauberite crystal 237
131 Thenardite crystal 237
132 Thenardite twinned 237
133. Bante crystals 239
134. Bante crystals 240
135. Celestite crystals 241
136 Anglesite crystal 243
137. Anglesite crystal 243
138 Anglesite crystal 243
139. Gypsum crystals 247
140. Gypsum twinned 247
141. Gypsum twinned 248
142. Epsomite crystal 250
143. Hanksite crystal 252
144. Crocoite crystals 253
145. Scheelite crystal . 255
146. Scheelite crystal 255
147 Wulfemte crystal 257
148 Wulfemte crystal , . 257
149 Wolframite crystal 250
150. Monazite crystal , 264
151 Xenotime -crystals 265
152 Apatite crystal , 267
153 Apatite crystal . . 267
154- Vanadimte crystal . 262
155. Skeleton crystal of vanadmite . .272
156 Amblygomte crystal , 2^
157. Lazulite crystals , . , . 2^6
158 Olivemte crystal. , 27^
159 Skorodite crystal 286
160 Radiate wavelhte on a rock surface . , , 287
161. Columbite crystals . , ^
162 Samarskite crystals « . . . , > . 297
163 Olivme crystals , , 3P3
164 Willemite crystal , , 3O7
165 Phenacite crystal , 3Og
166. Garnet crystal (natural size) . 3IO
167 Garnet crystals ,, , , .310
168 Garnet crystal , 31O
16^) Nephehue crystal, , I
LIST OF ILLUSTRATIONS
Xv
PAGE
. ,
170 Zircon crystals ....... .317
171 Zircon twinned „.
172 Thorite crystal 3Ip
173 Andalusite crystals ,2O
174 Topaz crystals 32-
175 Topaz crystal 323
176 Topaz crystal ,24
177 Danbunte crystal 325
178 Zoisite crystal ^
179 Epidote crystal ^2g
1 80 Epidote crystals 328
181 Chondrodite crystal 333
182 Datolite crystal 334
183 Staurolite crystal 337
184 Staurolite crystal twinned 337
185 Staurolite crystal twinned 33-7
1 86 Sodalite mterpenetration twin of t\vo dodecahedrons 340
187 Prehmte crystal - 344
1 88. Axinite crystal 346
189 Axmite crystal . 346
190 Dioptase crystal 347
191 Percussion figure 348
192. Biotite crystal 349
193. Biotite twinned about a plane . 349
194 Etch figures 356
195 Muscovite crystal 356
196 Beryl crystals .. 360
197 Beryl crystals . . 360
198. Cross-section of pyroxene * , 363
199 Enstatite crystal. . 366
200 Wollastomte crystal * . 368
201. Augite crystal . . 37*
202. Augite twinned . 371
203 Interpenetration twin of augite . 371
204 Diopside crystals , . 372
205, Hedenbergite crystal 373
206* Acnute crystal , 3 76
207. Spodumene crystal. . . 379
208 Rhodonite crystals 3&>
209;. Ampibole crystals * 3^4
210. Kyanite crystals 394
211 Bladed kyanite crystals in a micaceous quartz schist 395
212. Calarmne crystals , 30
213. Orthoclase crystals . . . » , , ...... 410
xvi LIST OP ILLUSTRATIONS
FIGURE PAGE
214 Orthoclase crystals • • • • » 410
215 Carlsbad mterpenetration twins of orthoclasc 410
216 Contact twin of orthoclase according to the Carlsbad law 4IO
217 Baveno twins of orthoclase 411
218 Manebach twin of orthoclase 411
219 Section of mirocline viewed between crossed nicols 4x4
220 Adulana crystal 414
221 Albite crystals 419
222 Albite twinned 419
223 Albite twinned 419
224 Twinning stnations on cleavage piece of ohgoclasc 420
225 Albite twins with the crystal axis 420
226 Position of "rhombic sections" in albite . 420
227 Diagram of crystal of tnclimc feldspar f 420
228 Potash-oligoclase crystal 422
229 Scapohte crystals 424
230 Chntonite twinned according; to the mica law 427
231 Cknochlore crystal 430
232 Clmochlore twinned according to mica law 430
233 Chnochlore with same forms as m Fig 232 430
234 Clmochlore tnllmg twinned according to mica law 430
235 Pennimte crystal 430
236 Pennimte crystal twinned 430
237 Vesuviamte crystals . 433
238. Tourmaline crystals 436
239 Tourmaline crystals 436
240 Cooling crystal of tourmaline 436
241 Cordiente crystal . . , 439
242 Apophylhte crystals 444
243 Heulandite crystal , , 447
244 Heulandite, var beaumontJte . . 447
245 Philhpsite mterpenetration twin , , 448
246 Phillipsite , 448
247 Harmotome fourling twinned like pmllipsite . 449
248 Sheaf-like aggregates of stilbite , . 450
249 Laumontite crystal 452
250 Divergent groups of scolecite crystals 453
251 Scoleate crystal , 453
252 Natrohte crystals , , . 434
253. Thomsomte crystal . , ... 456
254 Chabazite crystal t 4^7
255 Chabazite mterpenetration twin . . 457
256. Phacohte with same form as in Fig 254 . 457
257 Analate crystal , t 4
LIST OF ILLUSTRATIONS
xvi
FIGURE PAGE
258 Analcite crystal . , , . , 4-9
259 Ilmemte crystal 463
260 Titanite crystal 4g4
261 Titanite crystal 4^4
262 Titanite crystal 454
263 Simple blowpipes 4gg
264 Bellows for use with blowpipe 468
265 Candle flame showing three mantles 47o
266 Reducing flame 4yZ
267 Oxidizing flame 4^r
268. Props and position of charcoal 4^5
DESCRIPTIVE MINERALOGY
PART I
GENERAL CHEMICAL MINERALOGY
CHAPTER I
THE COMPOSITION AND CLASSIFICATION OF MINERALS
Definition of Mineral. — A mineral is a definite inorganic, chem-
ical compound that occurs as a part of the earth's crust. It possesses
characters which are functions of its composition and its structure.
Most minerals are crystallized, but a few have been found only in an
amorphous, colloidal condition. These are regarded as gels, or solid
colloids.
The most essential feature of a mineral is its chemical composition,
since upon this are believed to be dependent all its other properties.
Chemical Substances Occurring as Minerals.— The chemical
substances found native as minerals may be classed as elements and
compounds The latter comprise chlorides, fluorides, sulphides, oxides,
hydroxides, the salts of carbonic, sulphuric, phosphorus, arsenic, anti-
mony and silicic acids, a large series of complicated compounds known
as the sulpho-salts, a few derivatives of certain metallic acids— the
aluminates and the ferrites— besides other salts of rarer occurrence,
some simple and others exceedingly complicated, and possibly many
solid solutions of gels or of a gel and a crystalloid. In some of these
classes all the compounds are anhydrous. In others, some groups are
anhydrous while the members of other groups contain one or more
molecules of water of crystallization.
The sulphides, chlorides and fluorides are derivatives of EfeS, HC1,
and ifeFs, respectively. They may be regarded as having been pro-
duced from these compounds by the replacement of the hydrogen by
metals. Illustrations: CuaS, CuS, NaCl, CaF2.
2 GENERAL CHEMICAL MINERALOGY
The hydroxides and the oxides may be looked upon as derivatives of
water, the hydroxides through the replacement of one atom of hydrogen
by a metal, and the oxides through the replacement of both hydrogen
/OH
atoms The mineral, bructte, according to this view is Mg/ ,
H(OH) X)H
derived from rr^rr\ by replacement of two hydrogen atoms in two
H(OH)
molecules of water by one atom of Mg Cuprite is >0, and tenonte
Cu/
CuO, the former derived by replacement of each atom of hydrogen m
one molecule of water by an atom of Cu, and the latter by replacement
of the two hydrogens by a single Cu
The salts of carbonic acid (H2COs) are the carbonates, those of sul-
phuric acid (HaSO*) the sulphates, those of orthophosphoric acid
(HsP04) the phosphates, those of orthoarsemc acid (HsAsO^ the arsen-
ates, those of orthoantimomc acid (HaSbO-i) the antimonates and those
of the silicic acids, the silicates There are, in addition, a few arsenites
and antimonites that are salts of arsemous (HsAsOa) and antimonous
(H3Sb03) acids
The principal silicic acids whose salts occur as minerals are normal
silicic acid (H4Si04), metasihcic acid (HaSiOj), and tribilicic acid
(HiSiaOs) The metasihcic and the tribihcic acids may be regarded
as normal silicic acid from which water has been abstracted, m the same
way that pyrosulphuric acid is ordinary sulphuric acid less H20, thus:
2H2SO*- H20 » H2S207
(HO)4Si-H20=H2Si03, metasihcic acid
3(HO)4Si-4H20=H4Si30«, tnsihcic acid.
Faydite is Fe2Si04, wollastonite, CaSiOs, and ortkoctase, KAlSisOs-
The alummates and ferntes may be regarded as salts of the hypothet-
ical acids AIO(OH) and FeO(OH), both of which exist as minerals,
the first under the name dtaspore and the second under the name
yO— A10
goethite. Spinel is the magnesium aluminate, Mg<f .(MgAfeO*),
\0-A10
and magnofernte the corresponding ferrate MgFe204. The very com-
X)— FeO
mon mineral magnetite is the iron ferrate Fe<; , or FesO*, In
X>-FeO
this compound the iron is partly in the ferrous and partly in the ferric
state.
COMPOSITION AND CLASSIFICATION 3
There are other minerals that differ from those of the classes above
mentioned in containing more or less water of crystallization These
are usually separated from those m which there is no water of crystal-
lization under the name of hydrous salts
Besides the classes of minerals considered there are others which
appear to be double salts, m which two substances that may exist
independently occur combined to form a third substance with prop-
erties different from those of its components Cryolite, sNaF-AlFa
or NasAlFe, is an example The sulpho-salts furnish many other
examples
Further, a large number of minerals are apparently isomorphous
mixtures of several compounds These are homogeneous mixtures
of two or more substances that crystallize with the same sym-
metry, and, consequently, that may crystallize together Their
physical properties are continuous functions of their chemical com-
positions. Other minerals are apparently solid solutions in one an-
other of simple crystallizable salts, of gels, of gels and salts, and of
gels and adsorbed substances Among these are some of the commoner
silicates.
Determination of Mineral Composition. — Since the properties
of minerals are functions of their chemical compositions, it is important
that their compositions be known as accurately as possible. It is
necessary in the first place that pure material may be secured for study
Pure material is most easily secured by making use of the differences
in density exhibited by different compounds The mineral to be studied
is pounded to a powder, sifted through a bolting doth sieve and shaken
up with one of the heavy solutions employed in determining specific
gravities. When the solution is brought to the same density as that
of the mineral under investigation all material of a higher specific gravity
will sink. The material with a density lower than that of the solu-
tion will rise to the surface Material with a specific gravity identical
with that of the solution will be suspended in it If the mixing is done
in a separating funnel of the proper type, the materials may be drawn
off into beakers in the order of their densities, and thus the pure mineral
may be separated from the impurities that were originally incorporated
with it. After the purity of the substance is assured by examination
under the microscope, it is ready for analysis
The composition of the purified material is determined by the
ordinary methods of chemistry known as analysis and synthesis.
In analysis the compound is broken into its constituent parts and
these are weighed, or it is decomposed and its constituents are trans-
4 GENERAL CHEMICAL MINERALOGY
formed into known compounds which are weighed From the weights
thus obtained the proportions of the components m the original sub-
stance may be easily calculated if the weight of the original substance
be known
In synthesis the compound is built up from known elements or
compounds
If the mineral caicite (CaCOs) is decomposed by heat into lime
(CaO) and carbonic acid gas (CCte), or if its components are trans-
formed into the known compounds CaSCU and KaCOj, the process is
analysis If the known substance CCfe is allowed to act upon the
known substance CaO and the resulting product is a substance possess-
ing all the properties of caicite, the process is synthesis.
Analytical Methods.— The analytical methods made use of in
mineralogy are (i) the ordinary wet methods of chemical analysis,
(2) the dry methods of blowpipe analysis, in which the mineral is
treated before the blowpipe without the use of liquid reagents except
to a very subordinate degree, and (3) microchemical methods, per-
formed on the stage of a compound microscope.
Blowpipe and microchemical analyses are made use of principally
for the identification of minerals By their aid the nature of the atoms
m a compound may easily be learned, but the proportions in which
these atoms are combined is determined only with the greatest difficulty.
The methods are mainly qualitative
Wet Analysis.— For exact determinations of composition the wet
methods of chemistry are usually employed, since these are the most
accurate ones They are identical with the methods described in
manuals of quantitative analysis, and therefore require no detailed
discussion here They are well illustrated by Prof Tschermak as
follows. If 734 mg. of the mineral goethite (in which qualitative tests
show the presence of iron oxide and water) are roasted in a glass tube,
water is given off This when caught and condensed m a second tube
containing dry calcium chloride increases the weight of this second
tube by 75 mg The residue of the mineral left in the first tube now
weighs about 660 mg An examination of this residue shows it to con-
sist exclusively of the iron oxide (FejjOs) Since only iron oxide and
water are present in goethite the sum of these two constituents ought to
equal the original weight of the mineral before roasting But 660+75 *
— 73SJ whereas the original weight was 734 The difference i mg. is|
due to unavoidable errors of manipulation. As it is very small it may"
be neglected in our calculations
The results of the analysis are generally expressed in percentages.
COMPOSITION AND CLASSIFICATION 5
which are obtained by dividing the weights of the different constituents
by the weight of the original substance
Thus: 660- 734= 89 92 per cent Fe20s
75"~734= 10 22 per cent EfeO
Total 100 14
The usual methods of analysis are, however, more indirect than this,
the components of the substance to be analyzed being first transformed
into known compounds and then weighed For instance, common salt
is known by qualitative tests to contain only Na and CL If 345 mg.
of the pure salt be dissolved in water and the solution be treated with
silver nitrate under proper conditions a precipitate of silver chloride
is formed so long as any sodium chloride remains in the solution. The
silver chloride is separated from the solution by filtration It contains
all the chloride present m the 345 mg of salt After drying, its weight
is determined to be 840 mg The solution from which the silver chloride
was separated contains all the sodium that was originally present in
the salt, but now it is in combination with nitric acid It contains
also any excess of silver nitrate that was added to precipitate the chlorine
NaCl + AgNOs - AgCl + NaN03
salt reagent precipitate filtrate
The filtrate is now treated with hydrochloric acid to precipitate
the excess silver The silver chloride precipitate is removed by filtra-
tion, leaving a solution containing sodium salts of nitric and hydro-
chloric acids besides some free acid of each kind. Sulphuric acid is
now added and the whole solution is evaporated to dryness. The free
acids are driven off by the heat and the sodium salts are transformed
into the sulphate, Na2S04 The residue consisting exclusively of NaaSO*
is now found to weigh 419 mg.
The 345 mg of salt have yielded 840 mg. of AgCl and 419 mg. of
NagS04 The silver chloride is known to contain 24 74 per cent of
chlorine and the sodium sulphate 32 39 per cent of sodium. The 840
mg of AgCl contain 207.8 mg of chlorine, and the 419 mg of
contain 135 7 mg. of sodium. Hence 345 mg of salt yield
207.8 mg. or 60.23 per cent Cl,
and 135 7 mg. or 3934 per cent Na
343.5 mg. 99.57 per cent
6 GENERAL CHEMICAL MINERALOGY
Records of Analyses. — The composition of minerals like that of
other chemical compounds is determined in percentages of their com-
ponents and is recorded as parts per 100 by weight. A weighed quantity
of themmeral is analy/ed, the products of the analysis are weighed and the
percentage of each constituent present is found by dividing its weight
by the weight of the original substance, as has already been indicated
In chemical treatises the results of the analyses are usually recorded
in percentages of the elements present. In mineralogical works it is
more common to write the percentage composition in terms of the
oxides of the elements, partly because the old analyses are recorded in
this way and partly because certain relations between the mineral
components can be better exhibited by comparison of the oxides than
by comparison of the elements present in them.
The record of the analysis of a magnestte may be given as.
Mg=2835 per cent,
Fe= 34 per cent,
0=14 25 per cent,
0=5698 per cent,
Total =99,92 per cent
or as
MgO=47 25 per cent,
FeO= 43 per cent,
C02=S2 24 per cent,
Total =99 92 per cent.
Calculation of Formulas. — After the determination of the per-
centage composition of a mineral, the next step is to represent this
composition by a chemical formula — a symbol which indicates the
relative number of elementary atoms in the mineral's molecule, instead
of the number of parts of its constituents in 100 parts of its sub-
stance.
The construction of a formula from the analytical results is simple
enough in principle, but in practice it is often made difficult by the
fact that many apparently pure substances are in reality composed of
several distinct compounds so intimately mtercrystalhzed that it is
impossible to separate them In the simplest cases the formula is
derived directly from the results of the analyses by a mere process of
division.
The atomic weights of the chemical elements are the relative weights
of the smallest quantities that may enter into chemical combination with
one another, measured in terms of the atomic weight of hydrogen which
is taken as unity, or of oxygen taken as 16. Thus the atomic weights
of nitrogen and oxygen are approximately 14 and 16 respectively, i.e.,
the smallest quantities of nitrogen and oxygen that can enter into com-
bination with each other and with hydrogen are in the ratio of the
COMPOSITION AND CLASSIFICATION
TABLE OF ATOMIC WEIGHTS
Element
Symbol
At Weight
Element Symbol
At. Weight
Aluminium
Al
27 i
Molybdenum
Mo
96 o
Antimony
Sb
120 2
Neodymium
Nd
144 3
Argon
A
3988
Neon
Ne
20 2
Arsenic
As
74 96
Nickel
Ni
58 68
Barium
Ba
137 37
Niton
Nt
222 4
Bismuth
Bi
208 o
Nitrogen
N
14 oi
Boron
B
II 0
Osmium
Os
190 9
Bromine.
Br
79 92
Oxygen
0
16 o
Cadmium
Cd
112 40
Palladium
Pd
106 7
Caesium
Cs
132 81
Phosphorus
P
31 04
Calcium
Ca
40 07
Platinum
Pt
195 2
Carbon
C
12 OOS
Potassium
K
39 10
Cerium
Ce
140 25
Praseodymium
Pr
1409
Chlorine
Cl
35 46
Radium
Rd
226 o
Chromium
Cr
52 0
Rhodium
Rh
102 9
Cobalt
Co
58 97
Rubidium
Rb
85 45
Columbium
Cb
93 5
Ruthenium
Ru
101 7
Copper.
Cu
63 57
Samanum
Sa
1504
Dysprosium
Dy
162 5
Scandium .
Sc
44 i
Erbium
Er
167 7
Selenium
Se
79 2
Europium
Eu
152 o
Silicon
Si
28 3
Fluorine
F
19 o
Silver
Ag
107 88
Gadolinium
Gd
157 3
Sodium
Na
23 o
Gallium
Ga
69 9
Strontium
Sr
8763
Germanium
Ge
72 5
Sulphur
S
32 06
Glucinum
Gl
9 i
Tantalum
Ta
181 5
Gold..
Au
197 2
Tellurium
Te
127 5
Helium
He
4 oo
Terbium
Tb
159 2
Holmmm.
Ho
163 5
Thallium
Tl
204 o
Hydrogen
H
i 008
Thorium
Th
232 4
Indium.
In
114 8
Thulium
Tm
168 5
Iodine. . .
I
126 92
Tin
Sn
118 7
Indium. .
Ir
193 i
Titanium
Ti
481
Iron
Fe
55 85
Tungsten
W
184 o
Krypton
Kr
82 92
Uranium
U
238 2
Lanthanum
La
139 o
Vanadium
V
51 06
Lead .
Pb
207 20
Xenon
Xe
130 2
Lithium....
U
6 94
Ytterbium (Neoytterbium)
Yb
173 5
Lutecium..
Lu
1750
Yttrium, .
Y
887
Magnesium. ..
Mg
24 32
Zinc .
Zn
65 37
Manganese. .
..Mn
54 93
Zirconium • »
,Zr
90 6
..,,Hg
200,6
8 GENERAL CHEMICAL MINERALOGY
values 14 1 6 : i l The quantities that possess these relative weights
are known as atoms Often the apparent ratios ot the elements in
combination are different from the uitios between their atomic weights,
but this is always due to the fact that one or the other of the elements
is present in more than its smallest possible quantity, i e , in a greater
amount than is represented by a single atom For instance, there are
several compounds of oxygen and nitrogen known, in which the weight
relations between the two elements may be represented by the follow-
ing figures 14 : 8, 14 : 16, 14 • 24, 14 : 32, and 14 : 40 If the
second of these compounds consists of one atom each of nitrogen and
oxygen, and these are the smallest quantities of the elements that
can exist in combination, the several compounds must be made up thus
14 : 8 14 . 16 14 . 24 14 : 32 14 * 40
N2O NO N203 N02 N205
for N can exist only in quantities that weigh 14, 28, 42 times as much
as the smallest quantity of hydrogen present in any compound, i e ,
the single atom, and 0 in quantities of 16, 32, 48, etc , times the weight
of the single hydrogen atom In order that even multiples of 14 and
1 6 shall exist in the ratios given above, their terms must be multi-
plied by quantities that will yield the following results.
28 . 1 6 14 : 16 28 48 14 32 28 : 80
which are the weights respectively of the numbers of atoms lepresented
in the above formulas
If, then, the elements combine in the ratio of their atomic weights,
or in some multiple of this ratio, the figures obtained by analysis must
be in one of these ratios, and consequently they furnish the data from
which the formula of the substance analyzed may be deduced In
gold chloride, for example, analysis shows the presence of 64 87 per cent
Au and 35 13 per cent Cl, i e , the gold and the chlorine are united in
the ratio of 64.87 ; 35 13 or -i-I. The combining ratio of single
tjj «5
atoms of gold and of chlorine is, however, 196 7 • 35 5, or -2—Z £Vi-
oo 5
dently in gold chloride the ratio of gold to chlorine is only one-third
as great as is the ratio between the atomic weights of these elements,
or the ratio of the chlorine to the gold three times as great. Hence
1 The atomic weight of hydrogen is more accurately i 008, when that of oxygen
is taken as 16
COMPOSITION AND CLASSIFICATION
9
there must be three times as much chlorine in gold chloride as would
be represented by a single atom of chlorine, or there must be three
atoms of chlorine in the compound, for we cannot imagine a quantity
of gold present which is equivalent to one-third of an atom of gold
Gold chloride is therefore AuCls
We can now prove our conclusion by calculation One atom of
gold and three atoms of chlorine ought to combine in the ratio of
1967:1065 (le, 355X3) If our conclusion is correct, and the
gold chloride analyzed is AuCls, then the quantities of gold and of
chlorine yielded by the analysis should be in this ratio The figures
obtained are in the ratio of 64 87 : 35 13 Multiplying both terms of
this ratio by 3 031 we obtain 196 62 . 106 5, which is approximately
the ratio expected.
In practice, the same result as that outlined above is reached by
dividing the results of analyses by the atomic weights of the various
elements or groups of elements concerned The quotients represent the
proportional numbers of the elements or groups present. If the small-
est quotient is assumed as unity, the ratios existing between this and
the other quotients indicate the number of atoms or groups of
atoms represented by the latter.
Illustrations,
Gold Chloride Result of Analysis Atomic Weights Quotients
Au = 64 87 per cent — 196 7 = 3298 =
Cl * 35 13 35 5 - 9896 =
Tin Chloride
Sn
Cl
45 26 per cent - 117 4 = 384
54 74 35 5 = * 542
Ratios
I
3
4 04
The formula of the gold chloride is AuCls, and of the tin chloride,
SnCU
Magnesium carbonate on analysis may yield: C= 14.26, Mg= 28 37;
Fe=.34, 0=5703, or, if recorded m the form of oxides: 002=52.24,
MgO=47 25, FeO= 43 From either of these results the formula is
easily obtained by the method described.
C=i4 26—11 97=1 188=1 009,
Mg= 28 37- 23.94= i 186=1.000,
Fe~ .34-5588= .006= .006,
0=57.03-15 96=3 573=3-°i2,
or,
MgCOs, if we neglect the small
quantity of iron present
10 GENERAL CHEMICAL MINERALOGY
From the second set of figures we have*
0)2=5224-4389=1 19 = 1, ] or>
MgO=47 25— 3990=1 184=1, r MgO C02, which is the same as
FeO= 43—7184= 006, J MgCOs, written in a different way
All formulas are derived by methods like these, but in many cases
the processes are made more difficult by the impossibility of deciding
positively whether those substances that are present in small quantities
are present as impurities or whether they exist as essential parts of
the compound
Formulas of Substances Containing Two or More Metallic
Elements or Acid Groups. — In the illustration given above the com-
pounds consist of but one kind of metallic element combined with one
kind of acid Often in the case of minerals there are present two or
more metallic elements, and less commonly several acid groups. When
two metals are present in definite atomic proportions the formula is
written in the usual manner, as CaMg(COs)2 for the mineral dolomite,
in which calcium and magnesium are present in the ratio of one atom
of each to two parts of the acid group COa. Very often, and perhaps in
the majority of cases, when two or more metallic elements are present
in different specimens of a mineral they are not found always in the
same proportion — the mineral may consist of isomorphic mixtures
of several substances For instance, many calcium-magnesium car-
bonates are known in which the ratio of calcium to magnesium present
is not as i atom to i atom, but in which this ratio is as 2 atoms
to i atom, 3 atoms to 2 atoms, or a ratio which would have to be
represented by irrational figures like 2 7236 atoms to i 5973 atoms
Each one of these compounds properly requires a separate formula,
as aCaCOa+MgCOs, 3CaC03+2MgCO3, etc , but practically the entire
series of compounds is represented by a single symbol, thus (Ca Mg) COs,
indicating that in the series we have to do with mixtures of carbonates
of calcium and magnesium, or with complex molecules containing in
different instances different proportions of the two carbonates. For
greater defimteness the symbol of the characteristic element of the
substance which is in largest quantity in the compound is usually written
first, as (Ca Mg)COs, when calcium carbonate is m excess, or
(Mg Ca)COs when pnagnesmm carbonate predominates If still greater
defimteness is desired small figures are placed below the symbols of the
elements concerned, as (Ca2 Mgi)COs or (Ca3 Mg2)C03, to indicate
the respective proportions present. (Ca2 Mgi)COs signifies that the
COMPOSITION AND CLASSIFICATION 11
mineral thus represented contains calcium and magnesium in the
ratio of 2 atoms of the former to i of the latter
Compounds Containing Water.— Often salts that separate from
aqueous solutions combine with certain definite proportions of water
Sometimes this water combines with the anhydrous portion of the com-
pound to form a double salt, as MgSO4+7H20, or MgS04 7H20
At other times a portion of the water, in the form of the group (OH),
called the hydroxyl group, occupies the place usually occupied by
a metallic element, and, occasionally, that usually occupied b> an
acid group, or by oxygen, as in Mg(OH)2
Water of Crystallization.— Double salts composed of an anhydrous
portion combined with water are usually well crystallized Although
the water appears in many cases to be but loosely combined with the
remainder of the compound it is an essential part of its crystal particle,
for by the loss of even a portion of it the crystal system of the compound
is often changed Water in this form is known as water of crystalliza-
tion, and the compounds are designated hydrates
The magnesium sulphate MgSO* 7HaO forms orthorhombic crystals
By evaporation of a hot solution of this substance the sulphate
MgSO4 6H20 separates as monochmc crystals.
Gypsum is CaSOi 2H2O Its crystallization is monoclinic When
heated to 200° it passes into the anhydrous orthorhombic mineral
anhydrite, CaS04
Water of crystallization may frequently be driven from the com-
pound in which it exists by continued heating at a comparatively low
temperature. It is usually given off gradually — an increase in the tem-
perature causing an increase in the quantity of water released until
finally the last trace disappears In many instances such a very high
temperature is required to drive off the last traces of the water that it
would appear that some of it is held m combination in a different
manner from that in which the remainder is held Indeed, it is not at
all certain that double salts containing water of crystallization are
different in any essential respect from ordinary atomic molecules in
which hydrogen and oxygen are present in atomic form.
Combined Water.— Water of crystallization is thought of as
existing in the compound as water because of the ease with which it
can be driven off Compounds in which the hydroxyl group is present
yield water only upon being heated to comparatively high temperatures
In them the elements of water are present, but not united as water.
When freed from their combinations with the other constituents of the
compound by heat they unite to form water Because its elements
12 GENERAL CHEMICAL MINERALOGY
are thought of as closely combined with the other elements in the
molecule, this kind of water is often distinguished from water of crystal-
lization by the term combined water.
Bructte (Mg(OH)2) and malachite (Cu2(OH)2C03) are minerals
containing the elements of water When heated they yield water
according to the reactions Mg(OH)2 = MgO+H2O and Cu2(OH)2COs
= CuO+CuC03+H20.
Combined water is not only more difficult to separate from its com-
bination than is water of crystallization, but when the combination
is broken the chemical character of the original substance is radically
changed, as may be seen from the reactions above indicated. More-
over, combined water is given off suddenly, at a certain minimum
temperature, and not gradually as in the case of water of crystal-
lization.
Blowpipe Analysis. — Although blowpipe analysis serves merely to
identify the chemical components of minerals, it is a most important
aid to mineralogists in their practical work
Nearly all minerals may be recognized with a close degree of accu-
racy by their morphological and physical properties To distinguish
between several minerals that are nearly alike in these characteristics,
however, the determination of composition is often important In"
cases of this kind a single test made with the blowpipe will frequently
give the desired information as to the nature of some one or more of
the chemical elements present, and thus in a few moments the mmeial
may be identified beyond mistake
The apparatus necessary to perform blowpipe analysis is very
simple and the number of pieces few These, together with all the
reagents in sufficient quantity to determine the composition of hundreds
of minerals, may be packed into a box no larger than a common lunch
box (See pp 467-470)
For more refined work than the mere testing of minerals a larger
collection of both apparatus and reagents is necessary, but it no case
is the quantity of material consumed in blowpipe analysis as great as
when wet methods of analysis are used
Principles Underlying Blowpipe Analysis.— The principal phe-
nomena that are the basis of blowpipe work are the simple ones known
in chemistry as volatilization, reduction, oxidation, and solution
For volatilization experiments charcoal sticks and glass tubes are
used A blowpipe serves to direct a hot blast upon the assay. The
volatilized products collect on the cool parts of the charcoal which
they coat with a characteristic color, or upon the cooler portions of
COMPOSITION AND CLASSIFICATION 13
tlie glass tubes The sublimates that collect in the tubes may be tested
with reagents or examined under the microscope
Some volatile substances impart a distinct and characteristic color
to an otherwise colorless flame These may be tested in the direct flame
of the blowpipe
Oxidation and reduction experiments are usually performed either
on charcoal or in glass tubes Oxidations are effected in open tubes
and reductions in those closed at one end The products of the oxida-
tion or of the reduction are studied and from their characteristics the
nature of the original substance is inferred
The solution of bodies to be tested is often made in the usual man-
ner, i.e , by treatmg them with liquid reagents, but more frequently
it is accomplished by fusion of a small quantity of the body with borax
(Na2B407 ioH20) or microcosmic salt ((NH4)NaHPO4 4H2Q). The
molten reagent dissolves a portion of the substance to be tested and in
many cases forms with it a colored mass From the color of the mass
the nature of the coloring matter may be learned.
Although the underlying principles of blowpipe analysis are simple
the reactions that take place between the reagents and the assay are
often very complex.
More explicit details of the operations of qualitative blowpipe
analysis are given in Part III
Microchemical Analysis. — The processes of microchemical analysis
are limited in their application to the detection of a single element or,
at most, of a very few elements in small quantities of minerals. They
are employed mainly in deciding upon the composition of a substance
whose nature is suspected
The principle at the basis of all microchemical methods is the manu-
facture of crystallized precipitates by treatment of the mineral under
investigation with some reagent, and the identification of these pre-
cipitates through their optical and morphological properties.
In practice, a small particle of the mineral the nature of which it
is desired to know is placed on a small glass plate, which may be covered
with a thin film of Canada balsam to prevent corrosion, and is
moistened with a drop or two of some reagent that will decompose
it The solution thus formed is slowly evaporated by exposure to the
air The plate is then placed beneath the objective of a microscope
and the crystals formed during the evaporation are investigated Or,
after a solution of the assay is obtained there is added a small quantity
of some reagent and the resulting precipitate is studied under the
microscope. By their shapes and optical properties the nature of the
14 GENERAL CHEMICAL MINERALOGY
FIG i — Sodium Fluosilicate Crystals Magnified 72 diam (After Rosenbusch )
FIG 2 —Potassium Fluosihcate Crystals Magnified 140 diam, (After Rosenbusch )
COMPOSITION AND CLASSIFICATION 15
crystals produced is determined, and in this way the nature of the con-
stituents they have obtained from the mineral particles is discovered
A large number of reagents ha\ e been used m microchemical tests
each of which is best suited to some particular condition The most
generally useful one is hydrofluosihcic acid (H2SiFb). If small frag-
ments of albite and of orthoclase are placed on separate glass slips, such
as are used for mounting microscopic objects, and each is treated with
a drop of this reagent and then allowed to remain in contact with the
air lor a few minutes until the solutions begin to evaporate, those
portions of the solutions remaining will be discovered to be filled with
little crystals The crystals in the solution surrounding the albite are
hexagonal m habit (Fig i), while those in the solution surrounding
the orthoclase are cubes, octahedrons or combinations of forms belonging
to the isometric system (Fig 2). The former are crystals of sodium
fluosihcate and the latter crystals of the corresponding potassium salt
The albite, consequently, is a sodium compound and the orthoclase a
compound of potassium In similar manner, by means of this or of
other reagents the constituents of many minerals may be easily detected
The method, however, is made use of only in special cases, when for
some reason or other analytical methods are not applicable
Synthesis. — Synthesis is the opposite of analysis. By the analytical
processes compounds are torn apart, or broken down, whereas by syn-
thetical operations they are put together or built up Synthetic methods
are employed principally in the study of the constitution of minerals
and of their mode of formation, and in the investigation of the condi-
tions that determine the different crystal habits of the same mineral
The products of synthetic reactions are often spoken of as artificial
minerals because made through man's agency In many instances
these artificial minerals are identical in every sense with natural minerals
Consequently, they may often serve as material for study, when the
quantity of the natural mineral obtainable is too small for the purpose
Classification of Minerals. — Classification is the grouping of
objects or phenomena in such a manner as will bring together those
that a're related or that are similar in many respects and will separate
those that are different
Since minerals are chemical compounds whose properties depend upon
their compositions, then* most logical classification must be based upon
chemical relationships. But their morphological and physical properties
are their most noticeable features, and hence these should also be taken
into account in any classification that may be adopted. Probably
the most satisfactory method of classifying minerals is to group them,
16 GENERAL CHEMICAL MINERALOGY
first, in accordance with their chemical relationships and, second, m
accordance \\ith their morphological and physical properties
The first division is into the great chemical groups, as, for instance,
the elements, the chlorides, the sulphides, etc The second division
is the separation of these great groups into smaller ones comprising
minerals possessing the same general morphological features These
smaller groups may contain only a single mineral or they may contain
a large number of closely allied ones If the basis of the subgroupmg
is manner of crystallization, it follows that the members of subgroups
containing more than one member are usually isomorphous compounds
Thus the subdivisions of the great chemical groups are single minerals
and small or large isomorphous groups of minerals, arranged in the
order in which their metallic elements are usually discussed in treatises
on chemistry For example, the great group of carbonates embraces
all minerals that are salts of carbonic acid (EfeCO'j) This great group
is divided into smaller groups along chemical lines, as for instance, the
normal carbonates, the hydrous carbonates, the basic carbonates, etc
These smaller groups are finally divided into subgroups according to
their morphological properties — the normal salts, for example, being
divided into the two isomorphous groups known as the calcite and the
aragonite groups, and a third group comprising but a single mineral
In certain specific cases some other classification than the one
outlined above may be desirable For instance, in books written for
mining students it is often found that a classification based upon the
nature of the metallic constituent is of more interest than the more
strictly scientific one outlined above, because such a classification
emphasizes those components of the minerals with which the mining
student is most concerned In books written for the student of rocks,
on the other hand, the most important determinative features of minerals
are their morphological characters, hence m these the classification
may be based primarily on manner of crystallization
In the present volume the classification first outlined is used, but
because such a small proportion of the known minerals are discussed
the beauties of the classification are not as apparent as they would be
were ail described
CHAPTER II
THE FORMATION OF MINERALS AXD THEIR ALTERATIONS
The Origin of Minerals.— Minerals, like other terrestrial chemical
compounds, are the result of reactions between chemical substances
existing upon the earth When they are the direct result of the action
of elements or compounds not already existing as minerals they are said
to be primary products, when formed by the action of chemical agents
upon minerals already existing they are often spoken of as secondary,
though this distinction of terms is not always applied
Quartz (SiCb), formed by the cooling of a molten magma, is pnmar> ,
when formed by the action of water upon the siliceous constituents of
rocks it is secondary
The Formation of Primary Minerals — Minerals are produced in a
great variety of ways under a great variety of conditions Even the
same mineral may be produced by many different methods The more
common methods by which primary minerals are formed are precipita-
tion from a gas or a mixture of gases, precipitation from solution, the
cooling of a molten magma, and abstraction from water or air by plants
and animals
Deposits from Gases. — Emanations of gases are common in vol-
canic districts The gases escaping from volcanic vents are mainly
water vapor, hydrochloric acid, sulphur dioxide, sulphuretted hydro-
gen, ammonia salts and carbon dioxide, besides small quantities of other
gases and the vapors of various metallic compounds By the reactions
of these with one another or with the oxygen of the air, sulphur, salam-
momac (NHiCl) and other substances may be formed, and by their
reaction upon the rocks in the neighborhood halite (NaCl), ferric chlo-
ride (FeCls), hematite (Fe20s) and many other compounds may be
produced
The production of minerals through the reactions set up between
various gases and vapors is known as pneumatolysis Their separation
from the gaseous condition is known as sublimation Minerals formed
by sublimation are usually deposited as small, brilliant crystals on the
surfaces of rocks or upon the walls of cavities and crevices in them.
17
18 GENERAL CHEMICAL MINERALOGY
The reactions by %\hich they are produced are often quite simple. Thus
the reaction between sulphuretted hydrogen and sulphur dioxide yields
sulphur (2H2S+S02 = 3S+2H20), as does also the reaction between the
first named gas and the oxygen of the atmosphere (HjS+O = H2O+S)
Ferric chloride may be produced by the action of hot hydrochloric
acid upon some iron-bearing material deep within the earth's in-
terior This being volatile at high temperatures escapes to the air
as a gas Here it may react with water vapor, with the resulting for-
mation of hematite (2FeCl3+3H20=Fe203+6HCl) By the action
of carbonic acid gas upon volatile oxides, carbonates are formed,
(Fe203+2C02=2FeCOa+0) In other cases, however, the reactions
are very complicated
Precipitation from Solution. — Nearly all substances are soluble
to an appreciable degree in pure water An increase in temperature
usually increases the quantity of the substance that can be dissolved,
as does also an increase of pressure Moreover, the solubility of a
salt is increased on the addition of another salt containing no common
ion, and, conversely, is diminished in the presence of another having a
common ion Thus, gypsum (CaS04 2H20) is sparingly soluble in
water, but it becomes much more soluble upon the addition of salt
(NaCl) On the other hand, salt (NaCl) is much less soluble in water
containing a little magnesium chloride (MgClo) than it is in pure water.
When a solvent contains a maximum amount of any substance that
it may hold under a given set of conditions the solution is said to be
saturated From a saturated solution under ordinary conditions
precipitation results Upon the evaporation of the solvent, the lowering
of its temperature or of the pressure under which it exists, or the addi-
tion to the solution of a substance containing an ion already in the
solution. Of course, the addition of a substance which will react with
the solution and produce a compound insoluble m it will also cause
precipitation
The following table contains the results of various experiments on
the solubility of some common minerals
SOLUBILITY OF VARIOUS COMPOUNDS IN 100 PARTS PURK WATFR
(The results are given in parts by weight)
Halite (NaCl), at 7° 35 68 Calcitc (CaCO,), in the
Fluonte (CaF2), at 15^° 0037 cold 002
Gypsum (CaS04 2H20),ati5° 250 Strontiamte (SrCO,) in
Anhydrite (CaS04), in the cold 00025 the cold 00555
Celestite (SrS04), at 14° 015 Magnetite (Fte()4) 00035
FORMATION OF MINERALS 19
PERCENTAGES OF VARIOUS MINERALS SOLUBLE IN WATER \T 80°
(When treated 30 to 32 da\s)
Galena (PbS) 179 Chalcop>nte CCuFeS2) 1669
Stibmte (Sb2S3) 5 01 Bouraomte f(Pb Cu)SbS3) 2 075
Pynte (FeS2) 2 99 Arsenopynte (FeAsSj i 5
Sphalerite (ZnS) 025
So many substances that are usually regarded as insoluble are known
to be dissoh ed under conditions of high temperature and pressure that
no substance is behe\ ed to be entirely insoluble
Po\\dered apophylhte ((HK)2Ca(Si03)2 H20), which is a silicate
that is generally regarded as insoluble in water, is dissoh ed sufficiently
in this sohent at a temperature of i8o°-iQO° and under a pressure of
10-12 atmospheres to }ield crystals of the same substance upon cooling
Water containing gases or traces of salts is usually a more efficient
dissolving agent than pure water When the gases are lost, or the
salts are decomposed by reactions with other compounds, precipitation
may ensue
PARTS OF VARIOUS MINERALS DISSOLVED ix 10,000 PARTS OF VARIOUS
SOLUTIONS
Gold loses i 23 per cent of its \\eight when treated with 10 per cent soda
solution at 200°
One part gypsum (CaSO4 2H20) dissolves in 199 parts of saturated NaCl
solution Only 4 part dissolves in 200 parts pure \\ater
Pyt lie (FeSo) loses 10 6 per cent of its mass upon boiling for a long time
with a solution of Na2S Under the same circumstances galena loses 2 3
per cent
One of the commonest of the gases found in water on the earth's
surface is carbon dioxide This is an active agent in decomposing sili-
cates and in dissolving carbonates, so that water m which it is dissolved
is usually a more powerful solvent than pure water Its dissolving
power increases with the pressure, as in the case of pure water, but
diminishes with increasing temperature The action of carbonated
water on silicates is due to the replacement of the silicic acid by carbonic
acid and the production of bicarbonates, which are usually more soluble
than the corresponding carbonates The greater solubility of carbon-
ates, like calcite, in carbonated water is also due to the formation of
bicarbonates For example, the action of carbonated water upon cal-
cite (CaCOs) is as follows
CaC03+H20+C02=CaIfc(C03)2.
20 GENERAL CHEMICAL MINERALOGY
Carbonated water is more effective as a solvent under pressure
because of the inability of the CCb to escape under this condition When
pressure is removed the CCb escapes, or evaporation takes place, and the
reverse reaction occurs, as
CaH2(C03)2= CaC03+H20+CO2
The dissolving effect of carbonated water upon various carbonates
and other minerals and the influence of pressure and temperature upon
the solution of a carbonate are indicated in the three tables following
SOLUBILITY OP CERTAIN CARBONATES IN 10,000 PARTS OF CARBONATED
WATER
(The results are given in parts by weight)
Calcite (CaC03), at 10° 10 o Sidente (FcCO,) at 18° 7 2
Dolomite (CaMg(COs)2) at 18° 3 i Witherite (BaCOj) at 10° 170
Magnesite (MgCOs), at 5° 13 i Strontiamte (SrCOi), at 10° 12 o
PERCENTAGES OF \ARIOUS MINERALS SOLUBLE IN CARBONATFD WATLR
(When treated 7 weeks)
Adulana (KAlSiaOs) 328 Apatite (Ca«(F CIXPCX).) i 821
Ohgoclase Apatite (Cafi(F Cl)(POi)0 2 018
(NaAlSi308+ CaAl(SiO)4) 533 Olivme ((Mg Fe)2Si04) 2111
Hornblende (complex silicate) i 536 Magnetite (Fe304) 307 to i 821
Serpent] ne (KUMgsSi'Oo) i 211
INFLUENCE OF TEMPERATURE AND PRESSURE UPON THE SOLUTION OF
MAGNESIUM CARBONATE (MgC03) IN CARBONATED WATER
(The results are given m parts per 10,000 by weight)
i atmos at 19° 2 579 parts Temp 13 4° under i atmos 2 845 parts
32 3 730 29 3 2 105
56 4 620 62 o i 035
75 5 120 82 o 400
90 5 659 100 o ooo
Precipitation from Atmospheric Water —Rain is an active agent
in dissolving mineral matter Since it absorbs small quantities of carbon
dioxide, sulphur gases and other substances as it passes through the
atmosphere it may act upon many compounds, dissolving some, decom-
posing others and forming soluble compounds from those that would
otherwise be practically insoluble Moreover, it transports the dissolved
materials from one portion of the crust to some other portion, where,
under favorable conditions, they may be precipitated The rain water
that penetrates the earth's crust, dissolving and precipitating in its
FORMATION OF MINERALS
21
course through the crust, is known as vadose water It is an important
agent in ore-formation, since it may collect mineral matter from a great
mass of rocks and precipitate it in some favorable place, thus making
ore bodies
Deposits of Springs. — Springs are the openings at which under-
ground \\ater escapes to the earth's surface Much of the water flowing
from springs is the meteoric water which has circulated through the
crust and is again seeking the surface In its course through the crust it
dissolves certain materials Where it reaches the surface some of this
material may be dropped in consequence of (i) evaporation of the \\ater,
or (2) the escape of carbon dioxide, or (3) the oxidation of some of its
constituents through the action of the air, or (4) the cooling of the water
in the case of warm or hot springs
The deposits thus formed may occur as thin coatings on the rocks
over which the spring water passes, or as layers in the bottom of the
spring and the stream issuing from it Among the commonest minerals
thus deposited are calcite (CaCOs), aragomte (CaCOs), siderite (FeCOs)
and other carbonates, gypsum (CaSO-i 2H20), pynte (FeS2), sulphur
(S), and limonite (Fe4O3(OH)6) The carbonates are deposited largely
in consequence of the escape of C02 from the water, gypsum in conse-
quence of cooling, and limonite and sulphur through oxidation. If the
water contains EkS, this reacts
with the oxygen and a deposit _ 4 j,
of sulphur ensues (compare
P 18)
When the precipitation oc-
curs m cracks or fissures in the
rocks the precipitated matter
may partially or completely fill
the fissure, producing a vein, or,
the precipitated matter may fill
an irregular cavern forming a
bonanza It sometimes covers
the walls of cavities or the sur-
faces of minerals already exist-
ing, giving rise to a druse In
other cases precipitation may
occur while the solution is dripping from an overhanging surface,
making a stalactite, or the precipitate may fill the tiny crevices between
grains of sand cementing the loose mass into a compact rock
Mmerals produced by precipitation are often beautifully crystallized.
FIG 3 — Cross-section of Symmetrical Vein
(Aflts Le Neue Foster )
(a) Decomposed rock ($) Galena
(6) Quartz crystals (d) Sidente
22 GENERAL CHEMICAL MINERALOGY
At other times they form groups of needles yielding globular and other
imitative shapes, while in still other instances they occur as pulverulent
or amorphous masses The fillings of veins are often arranged sym-
metrically, similar materials occurring on opposite sides of their central
planes in bands, as shown in the figure (Fig 3) Some important ores
have been concentrated and deposited in this way
Deposits from Hot Springs.-— The water of hot springs deposits a
greater variety of minerals than that of cold springs Practically all
minerals that are soluble in hot water or in hot solutions of salts are
among them Among those of economic value may be mentioned
cinnabar (HgS) and stibnite (Sb2Ss)
Deposits from the Ocean and Lakes. — The water of the ocean and
of many lakes is rich in dissolved salts. That of lakes, however, is often
saturated or nearly so, while that of the ocean is not near the saturation
point. Consequently, while many lakes may deposit mineral sub-
stances, the ocean does not do so except under peculiar conditions When
a portion of the ocean is separated from the mam body of water, it may
evaporate and leave all of its mineral matter behind Lakes may also
completely evaporate with a similar result In each case the deposits
form layers or beds at the bottom of the basin in which the water was
collected.
In other instances the water brought to the ocean or a lake may
contain substances which will react with some of the materials already
present and produce an insoluble compound which will be precipi-
tated
Of course, the nature of the beds thus formed will depend upon the
character and proportions of the substances that were in the water
The ocean will yield practically the same kinds of compounds all over
the world and the beds deposited by the evaporation of ocean water
will be formed in nearly the same succession everywhere In the case
of enclosed bodies of water — like lakes or seas — in which the composi-
tion of the water may differ, the deposits formed may also differ
Many of the deposits formed in bodies of water are of great eco-
nomic importance and, consequently, are extensively worked Prob-
ably the most important are the beds of salt (NaCl) and of gypsum
(CaSO4 2H20), although borax (Na2B407 ioH20) was foimerly
obtained in large quantity from the deposits of some of the lakes in
the desert portions of the United States
In the following table are given the results of analyses of water of
the ocean and of Great Salt Lake, in Utah, calculated on the assump-
tion that the elements are combined in the manner indicated m the
FORMATION OF MINERALS
23
column on the left The results of the analyses of the waters of a few
noted lakes are given in the succeeding table
COMPOSITION OF SAXTS CONTAINED IN WATER OF THE OCEA.N AND GRE\T
NaCl
KCI
MgCL
CaS04
MgS04
Na2S04
LAKE
(Parts in 1000 of Water)
I II
27 3726 8 1163
5921 1339
3 3625 6115
1 3229 9004
2 2437 3 0855
RbCl2
MgBr2
Ca3(P04)2
CaC03
FeC03
Si02
0190
0547
0156
0434
0019
0149
0034
0081
0021
0780
OOII
0024
in
118 628
14 908
858
9 321
5 363
tr
35 0433
12 9427
149 078
I Water of N Atlantic off Norwegian Coast Anal>st, C Schmidt
II Average of Five Analyses, Caspian Sea at depths of from i m to 640 m
Analyst, C Schmidt
III Great Salt Lake, Utah Analyst, O D Alien
PERCENTAGE COMPOSITION or THE RESIDUES OF A FE\\ LAKE WATERS
Cl
Br
S04
C03
Na
K
Ca
Mg
Si02
etc
Total Solids
(per 1000
of Water)
Dead Sea
Lake Beisk, Siberia
Qoodenough Lake, B C
Borax Lake, Cal
64 49
22 79
7 64
32 27
1 45
tr
04
45
42 32
7 OS
13
61
41 41
22 47
15 75
31 32
36 17
38 10
3 24
1 01
6 65
1 52
4 09
07
02
03
10 53
1 86
04
35
tr
02
99
02
220 3
104 7
103 47
76 56
Deposits from Magmatic Water. — Equally important in depositing
mineral matter is the water that escapes from cooling lavas and other
molten magmas — designated as juvenile water All molten magmas
existing under pressure, i e , at some distance beneath the crust, contain
the components of water, which escape as the magma cools or when the
pressure diminishes, whether the diminution of the pressure is due to
24 GENERAL CHEMICAL MINERALOGY
the escape of the lava to the surface or to the cracking of the crust
In its passage to the surface the hot water carrying dissolved salts pene-
trates all the cracks and cavities in the rocks through which it passes
in its ascent and deposits its burden of material, forming veins and other
types of deposits Or, its components may decompose the materials
with which it comes in contact, replacing them wholly or in part by the
substances which it is carrying or by the products of decomposition
FIG. 4 —Cross-section of Vein in Green Porphyry The vein filling is chalcedonj
The white splotches are feldspar crystals The fairly uniform character of the
rock where not affected by the vein is seen on the right side of the picture The
rude banding parallel to the vein is due to changes that have proceeded out-
ward from the vein-mass into the rock
Since in many cases magmatic water contains corrosive gases, such as
fluorine, its action on the rocks which it traverses is profound A tiny
crack in the rocks may be gradually widened and the material on both
sides of it be replaced by new material, thus producing a vein which
is sometimes difficult to distinguish from a vein made in other ways
(Fig 4) This process is known as metasomatism, which is one kind of
metamorphism It is an important means of producing pseudomorphs
and bodies of mineral matter sufficiently rich in metallic contents to
constitute ore-bodies
FORMATION OF MINERALS 25
Solidification from Molten Magmas.— A molten magma, such as a
liquid lava, is probably a solution of various substances— mainly sili-
cates— in one another, or in a hot solvent Upon cooling or upon change
of conditions, such as may arise from loss of gas or water or from reduc-
tion of pressure, this hot solution graduall} deposits some of its con-
stituents as definite chemical compounds Upon further cooling other
compounds solidify and so on, until finally, if the rate of cooling has been
slo\\, the entire mass may separate as an aggregate of minerals— such
as constitute many of the rocks, as granite for instance, and main of the
lavas If the cooling has been rapid, some of the material ma\ separate
as definite minerals \\hile the remainder solidifies as a homogeneous
glass, as in the case of most lavas Sometimes the minerals thus formed
are bounded by crystal planes, but usually their growth has been so
interfered with that it is only by their optical properties that they can
be recognized as crystalline substances The nature of the minerals
that separate depends upon a great variety of conditions, the most
important of which is the chemical composition of the magma
In some cases the minerals separating from a magma tend to segre-
gate m some limited portion of its mass and thus produce an accumula-
tion that may be of economic value, le, the magma dijf a entities
Magnetite (FesGO, ilmenite ((Fe Ti)203), pynte (FeS2) and a few other
minerals are sometimes segregated in this way in very large masses
Metamorphic Minerals — Many minerals are characteristic of rocks
that are in contact with others that were once molten They were
formed by the gases and hot waters given off from the magmas before they
cooled The hot solutions with their charges of gas and salts penetrated
the pores of the surrounding rock and deposited in them some of their
material They reacted with some of the rock's components, producing
new compounds, and extracted others, leaving pores into which new
supplies of gas and water might enter In some cases the entire body
of the surrounding rock has been replaced by new material for some
distance from the contact Beyond this belt of most profound meta-
morphism are other belts in which the rock is less altered, until finally in
the outer belt is the unchanged original rock Into the outer contact
belt perhaps only gas penetrated and the changes here may be entirely
pneumatolytic Near the contact the changes may be metasomatic
Minerals formed by these processes near the contact of igneous masses
are frequently referred to collectively as contact minerals.
In other cases new minerals may be produced in rocks in consequence
of crushing attended by heat Hot water under high pressure
greatly facilitates chemical changes A part of the materials of the
26 GENERAL CHEMICAL MINERALOGY
crushed rock dissolves, reactions are set up and new compounds may
be formed The new minerals produced are more stable than the
original ones and have in general a greater density and consequently
a smaller volume The type of metamorphism that produces these
effects is kno\\n as dynamic metamot phtsm
Organic Secretions.— The transfer of mineral substances from a
state of solution to the solid condition is often produced through the aid
of organisms Mollusca, like the oyster, clam, etc , crustaceans, like
the lobster or crab, the microscopic animals and plants known as pro-
FIG 5 — Diorite Dike Cutting Granite Gneiss Pelican Tunnel, Georgetown, Colo.
(After Sptirr and Garry )
tozoans and algae and many other animals and vegetables abstract
mineral matter from the water in which they live and build up for them-
selves hard parts These hard parts, usually in the form of external
shells, are composed of calcium carbonate (CaCOs), either as calcite or
aragomte, of silica (8102) or of calcium phosphate Cas(P04)2. Although
not commonly regarded as minerals these substances are identical
with corresponding substances produced by inorganic agencies l
Paragenesis.— It is evident that minerals produced in the same
1 Plants and animals upon decaying yield organic acids which may attack minerals
already existing and thus give nse to solutions which may deposit pynte (FeSa),
hmomte (a hydrated iron oxide) or some other metallic compound This process,
however, is properly simply a phase of deposition from solutions
FORMATION OF MINERALS 27
\\ay \\ ill generally be found together. A certain association of minerals
will thus characterize deposits from magmas, another association
FIG 6 — Vein in Griffith Mine, Georgetown Colo , Showing Two Periods of Vein
Deposition (After Spwr and Garry )
gn = wall rock 6 = sphalerite c — chalcopynte
ff = comb quartz p = pynte g = galena
Balance^of vein-filling is a mixture of manganese-iron carbonates
15
10
It \Z
13 SH-
FIG 7 Vein Forming Original Ore-Body, Butte, Mont (After W.H Weed)
(i) Fault breccia, (2) ore, (3) altered granite, (4) first-class ore, (5) crushed quartz and
bormte, (6) fault clay, (7) solid pyrite and bormte, (8) crushed quartz and pynte, (9) solid
enargite ore with bormte, (10) banded white quartz and bormte, (n) white quartz, 6 inches,
(12) solid bormte, (13) solid pynte with bormte and quartz blotches, (14) bormte, (15) granite.
those precipitated from water, another those produced by contact
action, etc This association of minerals of a similar origin is known
28
GENERAL CHEMICAL MINERALOGY
as their paragenesis From a study of their relations to one another the
order of their deposition may usually be determined
Occurrence. — The manner of occurrence of mineral substance is
extremely varied, as may be judged from the consideration of the vari-
ous ways in which they are formed Deposits laid down in water occur
in beds or in the cement uniting grains of sand, etc , such as the beds
of salt (NaCl) or gypsum (CaSO* 2H20) found in many regions Those
produced by the cooling of magmas may form great masses of rock
such as granite, \vhich when it occurs as the filling of cracks in other
rocks is said to have the form of a dike (Fig 5) Deposits made by
water, whether meteoric or mag-
matic may give rise to veins, which
may be straight-walled or branch-
ing, like the veins of quartz (Si02)
that are so frequently seen cutting
various siliceous rocks When the
veins aie filled by meteoric water
they often have a comb-structure —
the filling consisting of several sub
stances arranged in definite layers
following the vein walls (see p 21)
If the composition of the depositing
solution, whether meteoric or mag-
matic, has remained constant for a
long time the vein may be filled
with a single substance It its com-
position changed during the time
the filling was in progress the layers
are of different kinds Further, it
deposition continued uninterruptedly
the layers may match on opposite
sides of the vein and the succession
may be the same from walls to center If, however, after the partial
or complete filling of the crack it was reopened and the new crack was
filled, the new vein when filled would be unsymmetncal if the new crack
occurred to one side of the center of the original vein (Fig 6) Repeated
reopening may give rise to a vein that is so lacking in symmetry that
it is difficult to trace the succession of events by which it was produced
(Fig 7) Veins filled by magmatic water are frequently more homo-
geneous.
Druses (Fig 8) arise when deposits simply coat the walls of fissures.
FIG 8 —Druse of Smithsomte (ZnCO3)
on Massive Smithsomte
FORMATION OF MINERALS
29
In many cases they may be regarded as veins, the development of which
has been arrested and never completed When the deposits coat the
walls of hollows within rocks they are known as geodes (Fig 9) Geodes
are common in limestones and other easily soluble rocks in \*hich
cavities may be dissolved
Gases and water under great pressure may penetrate the micro-
scopic pores existing in all rocks and there deposit material which may
fill the pores and cement the rocks If the deposited material is metallic
the rocks may be transformed into masses sufficiently rich in metallic
matter to become ore-bodies A body of this kind is known as an
impregnation It is well represented by some of the low grade gold
ores, such as those in the Black Hills
When rocks are decomposed bv the weather they are broken up
FIG 9 —Geodes Containing Calcite (CaCOs) Crystals
The rains wash the disintegrated substance into streams In its course
downward to lakes or the ocean, the heavier fragments, such as metallic
particles, may settle while the lighter portions are carried along
Thus the heavy parts may accumulate in the stream bottoms These
materials, consisting of gold, magnetite, garnet, pyrite and other min-
erals of high specific gravity, form a loose deposit m the stream bed
which is known as a placer. Gold is often found in placer deposits
The lighter portions may be carried to the lake or sea into which the
streams enter and may accumulate as sand on beaches and on the
bottom near the shores as gravel, sand, silt, etc Most sand consists
principally of quartz, but many sands contain also grains of feldspar
and other silicates, and sometimes other compounds
30 GENERAL CHEMICAL MINERALOGY
Alteration of Minerals.— Minerals, like living things, are constantly
subject to change Circulating waters may dissolve them in part,
or completely, and transport their material to a distant place, there
depositing it either in the form it originally possessed or in some new
form On the other hand, the mineral substance may be decomposed
into several compounds some of which may be carried off, while others
are left behind Again, the material remaining behind may com-
bine with other matter held in the water causing the decomposition,
and may form with it a new mineral or a number of different minerals
occupying the place of the original one This is m part metasomatism
The atmosphere may also act as a decomposer of minerals Through
the agency of its oxygen it may cause their oxidation, or it may cause
them to break up into several oxidized compounds Through the agency
of its moisture, it may dissolve some of these secondary substances or
it may form with them hydrated compounds The substances thus
formed may be dissolved in water and carried off, or they may remain
to mark the place of the mineral from which they were derived
Water, containing traces of salts, or gases in solution are exceedingly
active agents in effecting changes in minerals Many examples of the
alteration of practically insoluble minerals under the influence of dilute
solutions are known Calcite (CaCOs), for instance, when acted upon
by a solution of magnesium chloride (MgCb) takes up magnesium and
loses some ©f its calcium Monticelhte (CaMgSi04) when acted upon
by solutions of alkaline carbonates breaks up into a magnesium silicate
and calcium carbonate. Dilute solutions of various salts are constantly
circulating through the earth's crust and are there effecting trans-
formations in the minerals with which they come in contact On, or
near, the surface the transformations are taking place more rapidly
than elsewhere because here the solutions are aided in their decompos-
ing action by the gases of the atmosphere
The effect of the air in causing alteration is seen in the green coat-
ing of malachite ((CuOH^COs) that covers surfaces of copper or of
copper compounds exposed to its action In this particular case the
coating is due to the action of the carbon dioxide and the moisture of
the atmosphere. Other substances in contact with the air are coated
with their own oxides, sulphides, etc.
Pseudomorphs —When the alteration of a mineral has proceeded
in such a manner that the new products formed have replaced it particle
by particle a pseudomorph results Sometimes the newly formed sub-
stance crystallizes as a single homogeneous gram filling the entire
space occupied by the original substance Usually, however, the alter-
FORMATION OP MINERALS
31
ation begins along the surfaces of cracks or fissures in the body under-
going alteration, or upon its exterior, thus producing the new material
at several places contemporaneously (Fig 10) When the replace-
ment takes place m this manner the resulting mass is a network of
fibers of the new substance or an aggregate of grains with the outward
form of the replaced mineral
With respect to their method of formation chemical pseudomorphs
may be classified as alteration
pseudomorphs and replacement
pseudomorphs
Alteration Pseudomorphs. —
Pseudomorphs of this class may
be defined as those which retain
some or all of the constituents of
the original minerals from which
they were derived.
Paramorphs. — Pseudomorphs
composed of the material of the
pseudomorphed substance with-
out addition or subtraction of
any component are known as
paramorphs.
Paramorphism is possible only
in the case of dimorphous bodies.
It results from the rearrangement
into new bodies of the particles of which the original body was com-
posed.
Illustrations Calcite (hexagonal CaCOs) after aragomte (ortho-
rhombic CaCOs), orthorhombic sulphur after the monoclinic variety.
Partial Pseudomorphs. — The great majority of pseudomorphs
retain a portion, but not all, of the material of the original mineral
They may be formed by the addition of material to the original body,
by the loss of material from it, or by the replacement of a portion of
its material by new material
Pseudomorphs formed by the addition of substance to that already
existing are rare The substances most frequently added in the pro-
duction of such pseudomorphs are oxygen, sulphur, the hydroxyl
group (OH) and the carbonic acid group (CDs and COs)
Illustrations Malachite ((CuOH^COs) after copper, aoid argentvte
(Ag2S) after s^her.
Pseudomorphs resulting from the loss of material are not common.
FIG 10 — Alteration of Ohvine into Ser-
pentine The alteration is proceeding
from the surface of the crystal and
from surfaces of cracks that tra\erse
it The black specks and streaks
represent magnetite formed during the
process (After Tschermak )
32 GENERAL CHEMICAL MINERALOGY
They are caused by the abstraction of one or more of the constituents
of a compound
Illustration Native copper after cupnte (Cu20)
The greater number of partial pseudomorphs are formed by the sub-
stitution of some of the components of the original mineral by a new
material
Illustrations Limonite (Fe403(OH)6) pseudomorphs after sidente
(FeCOs) may be formed by the following reaction
4FeC03+ 20+3H20 = 4C02+Fe403(OH) 6
Cerussite (PbCOs) may be formed from galena (PbS), thus
PbS+40+Na2C03 = PbC03+Na2S04
Replacement Pseudomorphs. — Often the entire substance of a
mineral is replaced by new material, so that no trace of its original
matter remains In this case the nature of the pseudomorphed min-
eral can be discovered only from the form of the pseudomorph
Illustrations Quartz (Si02) after calcite (CaCOa) and gypsum
(CaSO4 2H20) after halite (NaCl)
Mechanical Pseudomorphs. — The processes described above as
originating pseudomorphs are chemical, and the resulting pseudomorphs
are sometimes designated chemical pseudomorphs There is another
class of pseudomorphs, however, in which the substance of a crystal
has not been replaced gradually by the pseudomorphing substance
In this class the pseudomorphing substance simply fills a mold left by
the solution of some preexisting crystal Thus, if a sulphur crystal
should become encrusted with a coating of bante (BaS04) and the
temperature should rise until the sulphur melts and escapes, there
would be left a mold of itself constructed of bante If, now, a solution
of calcium carbonate should penetrate the cavity and fill it with a deposit
of calcite (CaCOs), the mass of calcite would have the shape of a crystal
of sulphur. Pseudomorphs of this kind are known as mechanical
pseudomorphs
Weathering.—The term weathering is applied to the sum of all the
changes produced in minerals by the action of the atmosphere upon
them Although nearly all minerals show some traces of weathering,
these traces may often be detected only by the slight differences m color
exhibited by surfaces that have been exposed for a long time to the
action of the air when compared with fresh surfaces produced by frac-
ture or cleavage,
FORMATION OF MINERALS 33
The weathering of minerals is often of great economic importance
Veins of sulphides and a few other compounds may be oxidized where
they outcrop on the surface Some of the decomposition products thu?
formed may be soluble and others insoluble The insoluble products
may remain near the surface while the soluble ones are carried down-
ward by ground water along the course of the vein Here a reaction
may ensue between the soluble salts and the undecomposed portion of
the vein with the result that metallic compounds may be precipitated,
thus enriching the original vein matter and causing it to be changed
from a comparatively lean ore to one of great richness
Pynte veins on the surface are often marked by accumulations of
hmonite derived by the oxidation of the sulphide With this may be
mixed insoluble carbonates, silicates and other salts of valuable metals
present in the original sulphide Weathering may extend downward
along the veins for a short distance, replacing their upper portions with
the oxidized decomposition products This portion of a vein is often
spoken of as the o wdized zone, and this is sometimes the richest portion
of the vein It may be rich because less valuable substances have
formed soluble salts and have been drained away
Below the oxidized zone may be another zone less rich in valuable
compounds than the oxidized zone, but much richer than the material
below it The soluble decomposition products of the upper portion of
the vein may percolate downward, and react with the unchanged vein
matter, precipitating valuable metallic salts Although the original
vein matter may contain an inconsiderable quantity of the valuable
material, the precipitation in it of additional stores of material of the
same kind may raise the percentage of this constituent to a point where
it is profitable to mine it This belt of enriched ore is known as the
zone of secondary em ichment
The oxidized zone extends downward from the surface to a depth at
which the atmosphere and meteoric water become exhausted of their
oxygen — a depth which varies with local conditions The zone of
secondary enrichment extends from the bottom of the oxidized zone
to a short distance below the level of the ground water, beyond which
solutions will diffuse and thus be carried away from the vein. Below
the zone of enrichment the original vein-filling may reach downward
indefinite distances
Since many veins exhibit the features described, it follows that the
ore of many mines must grow poorer with depth, and that in many
instances the richest ore is near the surface
Some of the changes involved in weathering and secondary enrich-
34 GENERAL CHEMICAL MINERALOGY
ment of sulphide veins in limestone are indicated by the following reac-
tions in the case of a vein containing pyrite (FeS2), sphalerite (ZnS),
and galena (PbS)
(1) The first change produced at the surface may be the oxidation
of the sulphides to sulphates
(a) ZnS+40=ZnS04,
(b) PbS+40=PbS04 (anglesite);
(c) FeS2+70+H20=H2S04+FeS04
(2) These may react with the limestone as follows
(smithsomte) (gypsum)
(a) ZnS04+CaC03+2H20=ZnC03 + CaS04 2H20,
(cerussite) (gypsum)
(b) PbS04+CaCO3+2H20=PbC03 + CaS04
(3) Some of the sulphates and carbonates carried down into the un-
altered sulphides may react with these, yielding
Cgalena)
(a) PbS04+FeS2+02=PbS+FeS04+S02,
(galena) (sidente)
(J) PbC03+FeS2+02=PbS + FeCOs + S02;
(galena)
GO PbS04+ZnS = PbS+ZnS04,
(galena) (smithsonite)
(<0 PbC03+ZnS = PbS + ZnC03
The PbS replacing the ZnS and deposited in the cracks in the original
mixture of PbS, ZnS and FeS2 increases the percentage of this compound
in the vein and thus enriches it.
There is also an increase in the percentage of ZnS brought about by
the reactions between the zinc salts (ia and 20), and the pyrite, analogous
to those between the lead salts and pyrite (30 and 36) Thus
(sphalerite)
ZnS04+FeS2+02 = ZnS + FeS04+S02,
(sphalerite)
ZnC03+FeS2+02 = ZnS + FeC03+S02.
FORMATION OF MINERALS 35
The zinc salts produced in reactions $c and $d if carried downward will
also have the opportunity to react \\ith the pynte in the same way
If the ZnS is deposited in fissures in the vein matter this will tend to
enrich it with zinc
The oxidized zone contains (smithsonite) ZnCOs, (anglesite) PbSO4,
(cerussite) PbCOa and (limomte) Fe2(OH)2 The ZnS04, formed also
in the oxidized zone, is so readily soluble in water that it is leached from
the other oxidized compounds and is carried downward.
PART II
DESCRIPTIVE MINERALOGY
CHAPTER III
INTRODUCTION— THE ELEMENTS
OF the 1,000 or more distinct minerals recognized by mineralogists
only a few (some 250) are common A few are important because they
constitute ores, others because they are components of rock masses,
and others simply because of their great abundance Only a few miner-
alogists profess acquaintance with more than 500 or 600 minerals The
majority are familiar with but 300 or 400, relying for the identification of
the remainder upon the descriptions of them recorded in mmeralogical
treatises
Only the minerals commonly met with and those of economic or of
special scientific importance are described m this book They should
be studied with specimens before one, in order that the relation between
the descriptions and the objects studied may be forcibly realized Min-
eralogy cannot be studied successfully from books alone It is primarily
a study of objects and consequently the objects should be at hand for
inspection l
Mineral Names. — The names of the great majority of minerals end
in the termination "ite " This is derived from the ancient Greek suffix
"itis" which was always appended to the names of rocks to signify that
they are rocks The first portion of the name, to which the suffix is
added, either describes some quality or constituent possessed by the
mineral, refers to some common use to which it has been put, indicates
the locality from which it was first obtained, or is the name of some
person intended to be complimented by the mineralogist who first
described the mineral bearing it
1 Collections of the common minerals in specimens large enough for convenient
study may be secured at small cost from any one of the mineral dealers whose
addresses may be found m any mmeralogical journal
INTRODUCTION— THE ELEMENTS 37
The following examples taken from Dana illustrate some of these
principles The mineral hematite (Fe203) is so named because of the red
color of its powder, chlorite (a complicated silicate), because of its green
color, sidente (FeCOs), from the Greek word for iron, because it con-
tains this metal, magnetite (FeaO-i) after Magnesia in Asia, goethite
(FeO(OH)) after the poet Goethe
The names of a few minerals end in "ine," "ane," ^ase," ^ote," etc ,
but the present tendency is to ha\ e them all end in "ite " Occasionally,
the same mineral may have two names This may be due to the fact
that it was discovered by two mineralogists working at the same tune
in different places, or it may be due to the fact that the mineralogists of
different countries prefer to follow different precedents set by the old
mineralogists of their respective nationalities For example, the min-
eral (Mg Fe)sSi04 is called ohmne by the Germans and by most English-
speaking mineralogists, and peridot by the French The Germans follow
the German mineralogist Werner, who first used the name ohvine in
1789, while the French follow the French teacher Hauy, who proposed
the name peridot in 1801
ELEMENTS
The elements that occur in nature are few in number, and these,
with rare exceptions, do not occur in great abundance They may be
separated into the following groups the carbon group, the sulphur
group, the arsenic group, the silver group, and the platinum-iron
group Some of these comprise only a single mineral, while others
comprise six or seven Only a portion of these are described
THE NON-METALS AND METALLOIDS
CARBON GROUP
The carbon group embraces several minerals of which one is dia-
mond, another is an amorphous black substance known as schungite,
and the other two are apparently but different forms of graphite
The element may thereupon be regarded as tnmorphous Diamond
and graphite are both important.
Isometric (hextetrahedral) Hexagonal (ditngonal scalenohedral)
Diamond Graphite
Diamond (C)
The diamond is usually found in distinct crystals or in irregular
masses, varying m size from a pin's head to a robin's egg In some
cases large individual pieces are found but they "-are exceedingly rare
38
DESCRIPTIVE MINERALOGY
FIG ii — Etch Figures on
Cubic Face of Diamond
Crystal (After Tscher-
mak)
The largest ever found, known as the Cullman diamond (Fig 16),
weighed 3,024! carats or 621 grams, or i 37 Ib ,
and measured 112x64x51 mm It was cut
into nine fine gems and a number of smaller
ones (Fig 17)
In composition the diamond is pure car-
bon, but it is a form of carbon that is not
ignited and burned at low temperatures At
high temperatures, however, especially when
in the presence of oxygen, it burns freely
with the production of CC>2, and, in the case
of opaque varieties, a little ash
Its crystallization is isometric (hextetra-
hedral class), and the forms on the crystals often appear to be tetra-
hedrally hemihedral, although the
etch figures on cubic faces suggest
hexoctahedral symmetry (Fig n).
Octahedrons, tetrahedrons, icositet-
rahedrons and combinations of these
forms are common, and in nearly all
cases the interf acial edges are rounded
and the crystal faces curved Some-
times this curving is so pronounced
that the individuals are practically
spheres (Fig 12) Twins are com-
mon with 0(in) as the twinning
plane (Fig 13),
The cleavage of diamond is per-
fect parallel to the octahedral face.
This is an important characteristic, as the lapidary makes use of it
in the preparation of stones for cutting Its
fracture is conchoidal Its specific gravity is
3 52 and its hardness greater than that of any
other known substance Most diamonds are
dark and opaque, or, at most, translucent, but
many are found that are transparent and color-
less or nearly so Gray, brown, green, yellow,
blue and red tinted stones are also known, and,
with the exception of the blue and red diamonds,
these are more common than the colorless, or
luster of all diamonds is adamantine, and
FIG 12 — Crystal of Diamond with
Rounded Edges and Faces (Krantz )
FIG 13 — Octahedron of
Diamond Twinned
aboutO(m)
so-called white stones
INTRODUCTION—THE ELEMENTS 39
their index of refraction is very high, n=z 4024 for red rays, 2 4175 for
yellow rays, and 2 4513 for blue ra>s In consequence of their strong
dispersion, the reflection of light from the inner surfaces of transparent
stones is very noticeable, causing them to sparkle brilliantly, with a
handsome play of colors It is this latter fact and the great hardness
of the mineral that make it the most valuable of the gems The mineral
is a nonconductor of electricity
Three varieties of the diamond have received distinct names in
the trade These are
Gem diamonds, which are the transparent stones,
Bort, or Bortz, gray or black translucent or opaque rounded masses,
with a rough exterior and the structure of a crystalline aggregate, and
Carbonado, black, opaque or nearly opaque masses possessing a
crystalline structure, but no distinct cleavage
The only minerals with which diamond is liable to be confused
are much softer, and, consequently, there is little difficulty in dis-
tinguishing between them
Syntheses — Small diamonds have been made by fusing in an
electric furnace metallic iron containing a small quantity of carbon and
cooling the mass suddenly in a bath of molten lead They have also
been made by heating in the electric arc pulverized carbon on a spiral
of iron wire immersed m hydrogen under a pressure of 3,100 atmospheres
A third method, which resulted in the production of tiny octahedrons,
consisted in melting graphite in olivine, or in a mixture of silicates
having the composition of the South African " blue ground," with
the addition of a little metallic aluminium or magnesium
Occurrence and Origin — Diamonds are found (i) in clay, sand
or gravel deposits or in the rocks formed by the consolidation of these
substances, where they are associated with gold, platinum, topaz,
garnet, tourmaline and with other minerals that result from the decom-
position of granitic rocks, (2) in a basic igneous rock containing frag-
ments of shale (a consolidated mud) and (3) small diamonds have been
discovered in meteorites
The manner of origin of diamonds has been a subject of contro-
versy for many years The most popular theory ascribes the diamonds
in igneous rocks to the solution of organic matter m the rock magmas
and the crystallization of the carbon upon cooling Another theory
regards the carbon as an original constituent of the magma. The
diamonds in sand, sandstone, granite, etc , are believed to have been
transported from their original sources and deposited in river channels
or on beaches.
40 DESCRIPTIVE MINERALOGY
Localities — The principal localities from which diamonds are obtained
are the Madras Presidency in India, the Province of Mmas-Geraes in
Brazil, the Island of Borneo, the valleys of the Vaal and Orange
Rivers, and other places in South Africa, and the valley of the Mazarum
River and its tributaries in British Guiana Recently diamond fields
have been discovered in New South Wales, Australia, in the \alley of
the Kasai River m the Belgian Kongo, in Arkansas, and in the Tula-
meen district, British Columbia
In the United States a few gem diamonds have been found from
tune to time in Franklin and Rutherford counties in North Carolina,
in the gold-bearing gravels of California, and m soils and sands in the
states of Alabama, Virginia, Wisconsin, Indiana, Ohio, Idaho an^l
Oregon A stone (the Dewey diamond) found near Richmond, Virginia,
a few years ago is valued at $300 or $400
The principal source of diamonds and carbonado in Brazil at the
present time is Bahia, where the mineral occurs in a friable sandstone
along river courses The output of this region has decreased so greatly
in the last few years that although a mass of carbonado weighing 3,073
carats (the largest mass of diamond material ever found) was obtained
in 1895, the price of this impure diamond rose from $10 50 per carat
m 1894 to $36 oo per carat in 1896 and $85 oo per carat for the best
quality m 1916
The only diamond field of prominence m the United States is that
which has recently been exploited near Murfreesboro in Arkansas, where
the conditions are similar to those existing in South Africa The dia-
monds occur m a basic igneous rock (pendotite) that cuts through Scind-
stones and quartzites The pendotite is weathered to a, soft earth or
" ground " m which the diamonds are embedded Up to the end of
1914 over 2,000 diamonds had been found, mostly small stones weighing
in the aggregate 550 carats, valued at about $12,000 One, however,
weighed 8§ carats and another 7^ carats The rough unsorted stones
are valued at $10 per carat Three stones that were cut were found
to be worth from $60 to $175 per carat The district has not yet been
sufficiently developed to prove its commercial value The diamonds
in British Columbia occur in the same kind of rock as those m Arkansas
The few that have thus far been found are too small for any practical
use
In former times the mines of India and Borneo were very produc-
tive, the famous Golconda district m India for a long period furnishing
most of the gems to commerce
The African mines were opened in 1867 Since this time they
— mil, Ji/JjJkMIiJWTS 41
have been practically the only producers of gem material in the world
It is estimated that the quantity of uncut diamonds yielded by the
mines near Kimberly alone have amounted in value to the enormous
sum of $900,000,000 The output of the African mines in 1913 was
sold for about $53,000,000, being over 95 per cent of the world's out-
put of gem material Of this amount about $9,000,000 worth of stones
were furnished by German Southwest Africa, the balance by the
Union of South Africa The diamonds are found in a pendotite which
occurs in the form of volcanic necks, or " pipes," cutting carbonaceous
shales The igneous rock is much weathered to a soft blue earthy mass
known as " blue earth " Near the surface where exposed to the action
of the atmosphere the earth is yellow The diamonds are scattered
through the weathered material in quantities amounting to between
3 and 6 carat per cubic yard
E\tr action — Where the diamond occurs in sand and gravel it is ob-
tained by washing away the lighter substances
In South Africa and Arkansas the mineral is found in a basic volcanic
rock which weathers rapidly on exposure to the air The weathered
rock is mined and spread on a prepared ground to weather When suf-
ficiently disintegrated water is added to the mass and the mud thus
formed is allowed to pass over plates smeared with grease The dia-
monds and some of the other materials adhere to the grease, but most
of the valueless material is carried off by the water
Uses — Transparent diamonds constitute the most valuable gems
in use Perfectly white stones, or those possessing decided tints of red,
rose, green or blue are the most highly prized They are sold by
weight, the standard being known as the carat, which, until recently,
was equivalent to 3 168 grains or 205 milligrams At present the metric
carat is m almost universal use This has a weight of 200 milligrams
The price of small stones depends upon their color, brilliancy and size —
a perfectly white, brilliant, cut stone weighing one carat, being valued
at about $175 oo As the size increases the value increases in a much
greater ratio, the price obtained for large stones depending almost solely
upon the caprice of the purchaser
Nearly all the gem diamonds put upon the market are cut before
being offered for sale The chief centers of diamond cutting are Ant-
werp and Amsterdam in the Old World and New York in America
The favorite cuts are the brilliant and the rose For the former only
octahedral crystals, or those that will yield octahedrons by cleavage,
are used, for the rose cut distorted octahedrons or twinned crystals
In producing the "brilliant" a portion of the top of an octahedron is cut
42
DESCRIPTIVE MINERALOGY
off and a small portion of the bottom On the remainder are cut three
or four bands of facets running horizontally around the stone (see Fig 14)
The "rose" has a flat base surmounted by a pyramidal dome consisting
of 24 or more facets In late years the shapes into which diamonds are
cut have been determined less by the decrees of fashion and more by the
desire to sa\e as much ma-
terial as possible, and, conse-
quently, irregularly shaped cut
diamonds are much more
common than formerly (com-
pare Fig 17).
Diamonds are employed
also as cutting tools Small
fragments, or splinters of gem
quality, are used for cutting
and polishing diamonds and
Rose
Grona Back, or Pavilion
Step or Trap
Crown
Side View
Pavilion, or Base
Brilliant
FIG 14 — Principal " cuts " of Diamonds
other gems, and small crystals
with crystal edges for cutting
glass Small cleavage pieces
are utilized in the manufacture of engravers' tools and writing instru-
ments Recently diamonds with small holes of from 008 to 0006 of an
inch drilled in them, have been employed as wne dies
Bort is also used as a polishing and cutting material, while carbonado,
nearly all of which comes from Brazil, is used in the manufacture of
boring instruments Diamond drills consist of hollow cylinders of soft
iron set at their lower edges with 6, 8 or 12 black diamonds By rapid
revolution of this a "core" may be cut from the hardest rocks
Some Famous Diamonds — The largest diamond ever found — the Cull-
inan— was picked up at the Premier Mine (Fig 15) in the Transvaal in
January, 1905, and was presented to King Edward of England as a birth-
day gift in 1908 (Figs 16 and 17 ) It weighed about 3,025 carats (about
i 37 pounds) The next largest was found in June, 1893, at the Jagers-
fontem mine It is known as the Excelsior It weighed in its natural
state 971 carats and was 3 inches long in its greatest dimension It was
valued at $2,000,000 It is said to have been presented by the Presi-
dent of The Orange Free State to Pope Leo XIII The third largest
stone is the Reitz It is a 640-carat stone found at the same mine during
the close of 1895 This, though smaller, is said to be handsomer than the
Excelsior The most noted diamond in the world is the Kohmoor, which
weighed, before cutting, 186 carats It is now a brilliant of 106 carats,
belonging to the crown of England Other famous diamonds aie the
INTRODUCTION— THE ELEMENTS
43
FIG 15, — Premier Diamond Mines in South Africa
pIG X6,— -The Cullman Diamond. (Natural size )
DESCRIPTIVE MINERALOGY
FIG 17 — Gems Cut from the Cullman Diamond (Two-lifthb nat si/c )
Orlov, 193 carats, the property of Russia, the Regent or Pitt diamond
of 137 carats belonging to France, the Green diamond of Dresden,
weighing 48 carats, and the Blue
Hope diamond, weighing 44 carats
The " Star of the South," found in
Brazil, weighed 254 carats bcfoie
cutting and 125 .iftcnvard The
Victoria diamond from one of the
Kimberly mines -weighed 457 carats
\\hen found It has been cut to a
perfect brilliant of 180 carats valued
at $1,000,000 The Tiffany dia-
mond (Fig 1 8) now owned in New
York is a double brilliant of a
golden yellow color weighing 128^
carats (25 702 grams) and valued at
$100,000 When it is remembered
that a five-carat stone is large, the
enormous proportions of the above-named gems are better appreciated.
FIG 1 8 —-The Tiffany Diamond (Nat-
ural size ) (Kindness of TiJJany &• Co )
Graphite (C)
Graphite, or plumbago, occurs principally in amorphous masses of a
black, clayey appearance, in radiated masses, in brilliant lead black
scales or plates, and occasionally in crystals with a rhombohedral habit
Like diamond, graphite consists of carbon Crystals from Ceylon
yield C=794o, Ash=is 50, Volatile matter=s 10. The mineral is
often impure from admixture with clay, etc.
INTRODUCTION— THE ELEMENTS 45
Crystals of the material ar«e so rare that their symmetry is still in
doubt Their habit is hexagonal (ditngonal scalenohedral class)
Measurements made on the interfacial angles of crystals from Ticon-
deroga, New York, gave a c=i i 3859 These possess a rhombo-
hedral symmetry All crystals are tabular and nearly all are so distorted
that the measurements of their interfacial angles cannot be depended
upon for accuracy They apparently contain the planes R(ioTi),
OP(IOOO), COP2(II20), and 2P2(lI2l)
Graphite is black and earth} , or lustrous, according as it is impure
or pure It is easily clea\ able parallel to the basal plane and the cleav-
age laminae are flexible It is very soft, its hardness being only 1-2,
its density about 2 25 Its luster is metallic and the mineral is opaque
even in the thinnest flakes It is a conductor of electricity
Graphite is infusible and noncombustible even at moderately high
temperatures Like diamond, however, it may be burned under cer-
tain conditions at \ ery high temperatures (65o°-7oo°) It is unaffected
by the common acids and is not acted upon by the atmosphere
When, ho\\e\er, it is subjected to the action of strong oxidizing agents,
such as a \\arm mixture of potassium chlorate (KClOj) and fuming
nitric acid, it changes to a }ello\\ substance kno^n as graphitic acid
(CnKLiOj) It is thus distinguished from amorphous carbon, like
schungite and anthracite Moreo\er, man\ forms of graphite, \\hen
moistened with fuming nitric acid and heated, s\\ell up and send out
worm-like processes Those \\hich do not act thus are called graphititc
Natural graphite is of both types
Its color, softness and infusibility serve to distinguish graphite from
all other minerals but molybdenite (p 75) It ma\ be distinguished from
this mineral by the fact that it contains no sulphur
Syntheses — Crystalline graphite is made on a commercial scale
by treating anthracite coal or coke containing about 5 75 per cent of
ash in an electric furnace It also separates \\hen molten iron con-
taining dissolved carbon is cooled
Occurrence and Origin — Graphite occurs as thin plates and scales
m certain igneous rocks, m gneisses, schists and limestones, as large
scales m coarse granite dikes (pegmatite) and m crystalline limestones,
and as amorphous masses at the contacts of igneous rocks with carbona-
ceous rocks The mineral is also found in veins cutting sedimentary
and metamorphic rocks Crystals are found only in limestone
The occurrence of graphite m sedimentary and igneous rocks sug-
gests that it may have been formed m several ways It is thought
that the material in limestone and quartz-schist may represent carbo-
46 DESCRIPTIVE MINERALOGY
naceous material that was deposited with the sediments and which has
since been carbonized by heat and pressure The material m peg-
matite may be an original constituent of the magma that produced the
rock, and the graphite may be the product of pneumatolytic processes ,
i c , it may have been produced by deposits from vapors that accom-
panied the formation of the pegmatite If this be true, the mineral
found in metamorphosed limestone and schist may be of contact origin,
i e , it may have been produced by the migration of gases and solutions
from igneous rocks into the mass of the surrounding sediments The
vein deoosits probably had a similar origin, the mineral having been
deposited mainly in cracks traversing metamorphic rocks On the
other hand, graphite, in some instances, appears to be a direct separa-
tion from a molten magma
Localities — The principal foreign source of supply for commercial
graphite is the Island of Ceylon In the United States the mineral has
been mined on the southeast side of the Adirondacks in New York,
in Chester County, Pennsylvania, near Dillon, Montana, at several
points in Arkansas, Georgia, Alabama and North Carolina, in Wyo-
ming, in Baraga County, Michigan, and to a small extent in Colorado,
Nevada, and Wisconsin It occurs also abundantly at many other
places Its chief source in the United States is Graphite, near Lake
George, New York
Preparation — Graphite is obtained on a commercial scale by grind-
ing the rock containing it and floating the graphite flakes
Uses —Crude graphite, or plumbago, is used in the manufacture of
stove and other polishes, and of black paint foi metal surfaces, for both
of which it is especially valuable on account of its noncorrodmg propji-
ties The purified mineral is mixed with clay and made into crucibles
for use at high temperatures It is also ground and used m this form
as a lubricant for heavy machinery, and is compressed into u black lead "
centers for lead pencils
Production —The quantity of crude graphite mined m the United
States during 1912 amounted to 2,445 tons> valued at $207,033, besides
which there were manufactured 6,448 tons, valued at $830,193. The
imports were 25,643 tons, valued at $709,337
Schungjte is a black, amorphous carbon with a hardness of 3-4
and a spgr. of i 981 It is soluble in a mixture of HNOs and KClOj
without the production of graphitic acid. It occurs in some crystalline
schists.
INTRODUCTION— THE ELEMENTS
47
SULPHUR GROUP
Sulphur is known in at least six different forms, four of which are
crystalline The two best known forms crystallize respectively in the
orthorhombic (orthorhombic bipyramidal class) and the monoclimc
(prismatic class) systems The former separates from solutions of sulphur
in carbon bisulphide and the latter separates from molten masses
Both the orthorhombic and the monoclimc phases are believed to be
formed by natural processes, but the latter passes over into the former
upon standing, so that its existence as a mineral cannot be definitely
proven Selenium and tellurium, which are also members of the sul-
phur group, are extremely rare Tellurium occurs in rhombohedral
crystals and selenium in mixed crystals of doubtful character with
sulphur and tellurium
Sulphur (S)
Sulphur occurs in nature as a lemon-colored powder, as spherical or
globular masses, as stalactites and in crystals
Chemically it is pure sulphur, or a mixture of sulphur and clay,
FIG 19 FIG 20
FIG 19— Sulphur Crystals with P, in (£), 3?, 113 (s), P»°, on («), and oP,
ooi (c)
FIG 20 —Distorted Crystal of Sulphur (Forms same as in Fig. 19 )
bitumen or other impurities. It sometimes contains traces of tellu-
rium, selenium and arsenic
Crystals of sulphur are usually well formed combinations of ortho-
rhombic bipyramids and domes, with or without basal terminations.
Their axial ratio = 8108 * i i 9005 The principal forms observed
are P(in), POO(IOI), P £6(011), iP(ii3) and oP(ooi) (Figs 19 and
20) The habit of the crystals is usually pyramidal, though crystals
with a tabular habit are quite common
Crystals of sulphur are yellow Their streak is light lemon yellow,
48 DESCRIPTIVE MINERALOGY
The mineral has a resinous luster Its hardnebs is only i 5-2, and
density about 204 Its fracture is conchoidal and cleavage imper-
fect It is transparent or translucent, is brittle and is a non-
conductor of electricity Its indices of refraction for sodium light
area = i 9579, j8«a 0377, 7 = 2 2452
Massive sulphur varies in color from yellow to yellowish brown
greenish gray, etc , according to the character and amount of impurities
it contains Its powder is nearly always crystalline In mass it pos-
sesses a lighter color than the crystals or the massive sulphur
At a temperature of 114° sulphur melts, and at 270° it ignites,
burning with a blue flame and evolving fumes of SO 2 At about 97°
it passes over into the monoclimc phase It is insoluble in water and
acids, but is soluble in oil of turpentine, carbon bisulphide and chlo-
roform
There are few minerals that are apt to be mistaken for sulphur.
From all of them it may be distinguished by its bnttleness and by the
fact that it melts readily and burns with a nonlummous blue flame
Syntheses — Crystals with the form of the mineral are produced by
the evaporation of solutions of sulphur in carbon bisulphide, and also
by sublimation from the fumes of ore roasters
Occurrence and Origin — Sulphur occurs most abundantly m regions
of active or extinct \olcanoes, and in beds associated with limestone
and gypsum (CaSO* 2H20) In volcanic regions it is produced by
reactions between the gases emitted from the volcanoes, or by the reac-
tions of these with the oxygen of the air (seep 18) The deposits in
gypsum beds may result from reduction of the gypsum by organic
matter. Sulphur is formed also as a decomposition product of sulphides
In Iceland and other districts of hot springs sulphur is often deposited
in the form of powder as the result of reactions similar to those that
take place between the gases of volcanoes These hot springs are always
connected with dying volcanoes, being frequently but the closing
stages of their existence
Localities — The localities at which sulphur is known to exist are
very numerous Those of commercial importance are Girgenti m Sicily,
Cadiz in Spam, Japan, and in the United States, at the geysers 'of the
Napa Valley, Sonoma County, and at Clear Lake, Lake County,
California, at Cove Creek, Millard County, Utah, at the mines of the
Utah Sulphur Company in Beaver County, in the same State, at
Thermopohs, Wyoming, and at various hot springs in Nevada The
mineral occurs also abundantly in the Yellowstone National Park, but
cannot be placed on the market because of high transportation charges
INTRODUCTION— THE ELEMENTS 49
Its principal occurrence m the United States is at Lake Charles in
Calcasieu Parish, La , where it impregnates a bed of limestone at
a depth of from 450 to 1,100 feet It occurs also abundantly in the
coastal districts of Texas Here it is associated with gypsum
Extraction — Sulphur, when mined, is mixed with clay, earth, rock and
other impurities Until recently it was purified by piling in heaps and
igniting A portion of the sulphur burned and melted the balance,
which flowed off and was caught A purer product is ob tamed by dis-
tillation "Flowers of Sulphur" are made in this way At present
much of the sulphur is extracted by treating the impregnated rock m
retorts with steam under a pressure of 60 pounds and at a temperature
of 144° C The sulphur melts and flows to the bottom of the retorts
from which it is drawn off
In Louisiana and Texas, superheated steam is forced downward into
the sulphur-impregnated rocks. This melts the sulphur, which con-
stitutes about 70 per cent of the rock mass The melted sulphur is
forced to the surface and caught in wooden bins The crude material
has a guaranteed content of over 99! per cent sulphur
Uses — Sulphur, or brimstone, is used m the manufacture of some
kinds of matches, m making gunpowder, and m vulcanizing rubber
to increase its strength and elasticity It is used extensively in the
manufacture of sulphuric acid, but is rapidly giving way to pynte
for this purpose It is also utilized for bleaching straw, in the man-
ufacture of certain pigments, among \\hich is vermilion, and in the
preparation of certain medicinal compounds
Production — Most of the domestic product is at present from the
Calcasieu Pansh, La , where about 300,000 tons are mined annually.
New mines have been opened near Thermopolis in Wyoming, in Bra-
zona County, Texas, and at Sulphur Springs, Ne\ada. The total
amount of the mineral mined in 1912 was 303,472 tons, valued at $5,256,-
422 Besides, there were imported about 29,927 tons valued at $583,974,
most of which came from Japan Sicily is the largest producer of the
mineral, extracting about 400,000 tons annually.
ARSENIC GROUP
The arsenic group comprehends metallic arsenic, antimony, bismuth
and (according to some mineralogists), tellurium, besides compounds
of these metals with each other They all crystallize in the rhombo-
hedral division of the hexagonal system (ditrigonal scalenohedral class).
The only members of the group that are at all common are arsenic and
antimony
50 DESCRIPTIVE MINERALOGY
Arsenic (As)
Arsenic is rarely found in crystals It usually occurs massive or in
botryoidal or globular forms
Specimens of the mineral are rarely pure They usually contain
some antimony, and traces of iron, silver, bismuth, and other metals
The crystals are cubical in habit, with an axial ratio of i . i 4025
The principal forms observed are oR(oooi), R(ioTi), JR(ioT4),
— |R(oil2) and —^(0332) Twins are rare, with -|R(oil2) the
twinning plane
Arsenic is lead-gray or tin-white on fresh fractures, and dull gray or
nearly black on surfaces that have been exposed for some time to the
atmosphere
Crystals cleave readily parallel to the base The fracture of massive
pieces is uneven The mineral is brittle Its hardness is 3 5 and its
density 5 6-5 7 Its streak is tin-white tarnishing soon to dark gray
It is an electrical conductor
Arsenic may easily be distinguished from nearly all other minerals,
except antimony and some of the rarer metals, by the color of its fresh
surfaces From these, with the exception of antimony, it is also readily
distinguished by its action on charcoal before the blowpipe, when it
volatilizes completely without fusing, at the same time tmgeing the
flame blue and giving rise to dense white fumes of As20s, which coat the
charcoal The fumes of arsenic possess a very disagreeable and oppres-
sive odor, while those of antimony have no distinct odor
Syntheses — Arsenic has been obtained in crystals by subliming
arsenic compounds protected from the air It has also been obtained m
the wet way by heating realgar (As2Sa) with sodium bicarbonate at
300° C
Occurrence and Origin — Arsenic often accompanies ores of antimony,
silver, lead and other metals in veins in crystalline rocks, especially in
their upper portions, where it was formed by reduction from its com-
pounds
Locahties — The silver mines at Freiberg, and other places m Saxony
afford native arsenic in some quantity It is found also in the Harz, at
Zmeov in Siberia, in the silver mines of Chile and elsewhere.
Within the boundaries of the United States arsenic occurs only in
small quantity at Haverhill, N H , at Greenwood, Me , and at a silver
and gold mine near Leadville, Colo
Uses— Arsenic is used only in the forms of its compounds The
native metal occurs too sparingly to be of commercial importance.
INTRODUCTION— THE ELEMENTS 51
Most of the arsenic compounds used in commerce are obtained from
smelter fumes produced by smelting arsenical copper and gold ores
Antimony (Sb)
Antimony is more common than arsenic, which it resembles in many
respects It is generally found in lamellar, radial and botryoidal masses,
though rhombohedral crystals are known
Most antimony contains arsenic and traces of silver, lead, iron and
other metals
Its crystals are rhombohedral or tabular in habit, and have an axial
ratio of a : c=i . i 3236 The forms observed on them are the same
as those on arsenic with the addition of ocP2(ii2o), and several
rhombohedrons Twinning is often repeated The cleavage is perfect
parallel to oP(oooi)
Antimony exhibits brilliant cleavage surfaces with a tin-white color
On exposed surfaces the color is dark gray The mineral differs from
arsenic in its greater density which is 6 65-6 72, and in the fact that it
melts (at 629°) before volatilizing Its fumes, moreover, are devoid of
the garlic odor of arsenic fumes
Syntheses — Crystals of antimony are often obtained from the flues of
furnaces in which antimomal lead is treated. They have also been
made by the reduction of antimony compounds by hydrogen at a high
temperature
Occurrence and Localities — Antimony occurs in lamellar concretions
in limestone near Sala, Sweden, and at nearly all of the arsenic localities
mentioned above, especially in veins containing stibnite (Sb2Ss) or silver
ores It is found also in fairly large quantities in veins near Fredencton,
York County, New Brunswick, in California and elsewhere
Uses — Although the metal antimony is of considerable importance
from an economic point of view, being used largely in alloys, the native
mineral, on account of its rarity, enters little into commerce Some of
the antimony used m the arts is produced from its sulphide, stibnite
(see p 72) Most of the metal, however, is obtained in the form of a
lead-antimony alloy in the smelting of lead ores and the refining of pig
lead
Bismuth (Bi) is usually in foliated, granular or arborescent forms,
and very rarely in rhombohedral crystals, with a . c=i ' i 3036 It is
silver-white with a reddish tinge, is opaque and metallic Its streak is
white, its hardness 2-2 5 and density 98 It fuses at 271°. On charcoal
it volatilizes and gives a yellow coating It dissolves in HNOs When
52 DESCRIPTIVE MINERALOGY
this solution is diluted a white precipitate results The mineral occurs
in veins with ores of silver, cobalt, lead and zinc It is of no commercial
importance Most of the metal is obtained in the refining of lead In 1913
the United States produced 185,000 Ibs and Bolivia about 606,000 Ibs
Tellurium (Te) usually occurs in prismatic crystals with a tin-white
color and in finely granular masses in veins of gold and silver ores,
especially sulphides and tellundes Its hardness is 2 and density 6 2
Before the blowpipe it fuses, colors the flame green, coats the charcoal
with a white sublimate bordered by led, and yields white fumes
The mineral tellurium is of little value as a source of the metal
Most of that used in the arts is obtained as a by-product in the elec-
trolytic refining of copper made from ores containing tellundes and
from the flue dust of acid chambers and smelting furnaces The United
States, in 1913, produced about 10,000 Ibs of tellurium and selenium,
valued at $3^,000
THE METALS
The metallic elements occur as minerals m comparatively small quan-
tity, most of the metals used in the industries being obtained from their
compounds Iron, the most common of all the metals used in com-
merce, is rare as a mineral, as are also lead and tin Silver, copper, gold
and platinum are sufficiently important to be included in our list for
study Gold and platinum are known almost exclusively in the metallic
state A large portion of the copper produced in this country is also
native, and some of the silver
Silver, copper, lead, gold, mercury and the alloys of gold and mer-
cury crystallize in distinct crystals belonging to the isometric system
(hexoctohedral class) Platinum, as usually found, is in small plates
and grains Crystals, however, have been described and they, too, are
isometric Platinum and iron are separated from the other metals and,
together with the rare alloys of platinum with indium and osmium, are
placed in a distinct group which is dimorphous The reason for this is
that platinum, although isometric in crystallization, often contains
notable traces of indium, which in its alloy with osmium is hexagonal
(rhombohedral) Indium, thus, is dimorphous, hence platinum which
forms crystals with it and is, therefore, isomorphous with it, must also
be regarded as dimorphous The various platinum metals thus com-
pnse an isodimorphous group Iron is placed in the same group because
it is so frequently alloyed with platinum The metals are, therefore,
divisible into two groups, one of which comprises the metals named at
INTRODUCTION— THE ELEMENTS
53
the beginning of this paragraph and the other consists of the rare metals,
palladium, platinum, indium, osmium, iron and their alloys The
metal tin, which is tetragonal m its native condition, constitutes a third
group, but since it is extremely rare it will not be referred to again
GOLD GROUP
This group embraces the native metals, copper, siker, gold, gold-
amalgam (Au Hg), siher-amalgam (Ag Hg), mercury, and leal All
crystallize in the isometric system (hexoctahedral class), and all form
twins, with 0(in) the twinning plane Copper, silver and gold are
the most important
Copper (Cu)
Most of the copper of commerce is obtained from one or the other of
its sulphides A large portion, however, is
found native This occurs m tiny grams and
flakes, in groups of crystals and in large
masses of irregular shapes
In spite of its softness copper is better
crystallized than either gold or silver It is
true that its crystals are usually flattened and
otherwise distorted, but, nevertheless, planes
can very frequently be detected upon them
rr.i - i * , -, >v / \ FIG 2i.— Copper Crystal
The principal forms observed are oo O oo (100), ^^ M Q *^ * ,
oo O(no), 0(ni), and various tetrahexahedra 20 & 1 2io' (h).
and icositetrahedra. (Figs. 21 and 22 ) Some-
times the crystals are sim-
ple, in other cases they are
twinned parallel to O
Often they are skeleton
crystals Groups of crys-
tals are very common
These possess the arbo-
rescent forms so frequently
seen in specimens from
Keweenaw Point in Mich-
igan, or are groupings of
simple forms extended in
the direction of the cubic
FIG. 22. — Crystal of Copper from Keweenaw Point,
Mich , with wO(iio) and 202(211)
axes.
Cbpper is very ductile and very malleable Its hardness is only
54 DESCRIPTIVE MINERALOGY
2 5-3 and its density about 88 It possesses no cleavage, and its frac-
ture, like that of the other metals, is hackly In color it is copper-red
by reflected light, often tarnishing to a darker shade of red In very
thin plates it is translucent with a green color The metal fuses at
1083° and easily dissolves in acids It is an excellent conductor of elec-
tricity
Its most characteristic chemical reaction is its solubility in nitric
acid with the evolution of brownish red fumes of nitrous oxide gas
Copper may easily be distinguished from all other substances except
gold and a few alloys by its malleability and color It is distinguished
from gold by the color of its borax bead and by its solubility in nitric
acid with the production of a blue solution which takes on an intense
azure color when treated with an excess of ammonia From the alloys
that resemble it, copper may be distinguished by its greater softness and
the fact that it yields no coatings when heated on charcoal, while at the
same time its solution in nitric acid yields the reaction described above
Syntheses — Copper crystals separate upon cooling solutions of the
metal in silicate magmas and upon the electrolysis of the aqueous solu-
tions of its salts
Occurrence — The principal modes of occurrence of the metal are, (i)
as fine particles disseminated through sandstones and slates, (2) as solid
masses filling the spaces between the pebbles and boulders making up
the rock known as conglomerate, (3) in the cavities in old volcanic lavas,
known as amygdaloid, (4) as crystals or groups of crystals imbedded m
the calcite of veins, (5) in quartz veins cutting old igneous rocks or
schists, and (6) associated with the carbonates, malachite and azurite,
and with its different sulphur compounds, in the weathered zone of
many veins of copper ores
The copper that occurs in the upper portions of veins of copper
sulphides is plainly of secondary origin That which occurs in conglom-
erates and other fragmental rocks and in amygdaloids was evidently
deposited by water, but whether by ascending magmatic water or by
descending meteoric water is a matter of doubt
Localities — Native copper is found in Cornwall, England, in Nassau,
Germany, in Bolivia, Peru, Chile and other South American countries,
in the Appalachian region of the United States and in the Lake Superior
region, both on the Canadian and the American sides
The most important district in the world producing native copper is
on Keweenaw Point, in Michigan The mineral occurs mainly in a bed
of conglomerate of which it constitutes from i to 3 per cent, though it is
found abundantly also in sandstone and in the amygdaloidal cavities
INTRODUCTION— THE ELEMENTS 55
of lavas associated with the conglomerates Veins of caicite, through
which groups of bright copper en stals are scattered are also very plentiful
in many parts of the district The copper is nearh always mixed with
silver in visible grains and patches
Extraction and Refining —The rock containing the native metal is
crushed and the metal is separated from the useless material by wash-
ing The concentrates, consisting of the crushed metal mixed with
particles of rock and other impurities are then refined by smelting
methods or by electrolysis
Uses —The uses of copper are so many that all of even the important
uses cannot be mentioned in this place Both as a metal and in the form
of its alloys it has been employed for utensils and war implements since
the earliest times In recent times one of its principal uses has been for
the making of telegraph, telephone and trolley wires It is employed
extensively in electroplating by all the great newspapers and publishers,
and is an important constituent of the valuable alloys brass, bronze,
bell metal and German silver Its compound, blue vitriol (copper sul-
phate), is used in galvanic batteries, and its compounds with arsenic
are utilized as pigments
Production — The world's production of copper amounted to 1,126,-
ooo tons in 1912, but a large portion of this was obtained from its car-
bonates and sulphides The quantity obtained from the native metal is
unknown The contribution of the United States to this total was
about 621,000 tons, valued at about $206,382,500, of which 115,000 tons
was native copper from the Lake Superior region The largest single
mass ever found in the Lake Superior region weighed 420 tons
Silver (Ag)
Silver is usually found in irregular masses, in flat scales, in fibrous
dusters, and in crystal groups with arborescent or acicular forms
Sometimes the crystals are well developed, more frequently they ex-
hibit only a few distinct faces, but in most cases they are so distorted
that it is difficult to make out their planes
Pure silver is unknown The mineral as it is usually obtained con-
tains traces of gold, copper, and often some of the rarer metals, depend-
ing upon its associations.
Ideally developed silver crystals are rare They usually show
ooOoo(ioo), 006(110), 0(in) various tetrahexahedrons and other
more complicated forms The majority of the crystals are distorted by
curved faces and rounded edges, and many of them by flattening or
56 DESCRIPTIVE MINERALOGY
elongation The arborescent groups usually branch at angles of 60°,
one of the characteristic angles for groups of isometric crystals Twins
are quite common, with O(iii) the twinning plane
Silver is a white, metallic mineral when its surfaces arc clean and
fresh As it usually occurs it possesses a gray, black or bluish black
tarnish which is due to the action of the atmosphere or of solutions
The tarnish is commonly either the o\ide or the sulphide of silvci
The mineral has no cleavage Its fracture is hackly II is soft
(hardness 2-3), malleable and ductile, and is an excellent conductor
of heat and electricity Its density is about 10 5, varying slightly
with the character and abundance of its impurities It fuses at
960°
It is readily soluble in nitric acid forming a solution from which
a white curdy precipitate of silver chloride is thrown down on the
addition of any chloride This precipitate is easily distinguished from
the corresponding lead chloride by its insolubility in hot water
Synthesis — Crystals bounded by 0(in) and °o 0 oo (100) have been
made by the reduction of silver sulphate solutions, with sulphurous
acid
Occurrence — Native silver is found in veins with calcite (CaCOO?
quartz (8102), and other gangues traversing crystalline rocks, like
granite and various lavas, and also in veins cutting conglomerates
and other rocks formed from pebbles and sands It is also disseminated
in small particles through these rocks It occurs invisibly disseminated
in small quantities through many minerals, particularly sulphides,
and visibly intermingled with native copper It is abundant in the upper
weathered zones of many veins of silver-bearing ores, and m the zones
of secondary enrichment in the same veins It also occurs in small
quantity m placers In general, its origin is similar to that of gold
(see p 59)
Localities — The localities in which silver is found are too numerous
to mention Andreasberg in the Harz has produced many fine crys-
tallized specimens The principal deposits now worked are at Cobalt
in Canada, in Peru, in Idaho, at Butte, Montana, in Arizona and at
many places m Colorado On Keweenaw Point, in Michigan, fine
crystals have been found in the calcite veins cutting the copper-bearing
rocks, and masses of small size in the native copper so abundant in the
district Indeed some of the copper is so rich in silver that the ore
was in early times mined almost exclusively for its silver content At
present the silver is recovered from the copper in the refining process
At Cobalt the mineral occurs m well defined veins one inch to one foot
INTRODUCTION— THE ELEMENTS 57
or more in width, cutting a series of slightly inclined pre-Cambnan
beds of fragmental and igneous rocks The \eins contain native silver,
sulphides and arsenides of cobalt, nickel, iron and copper, caicite and a
little quartz Many of the veins are so rich (Fig 23) that Cobalt has
become one of the most important camps producing native silver in
the world.
Extraction and Refining — Silver is obtained from placers in small
quantity by the methods made use of in obtaining gold (see p 6i\
i e , by hydraulic mining When it occurs in quartz veins or m complex
ores such as constitute the oxidized portion of ore-bodies, the mass
may be crushed and then treated with quicksilver, which amalgamates
with the native silver and gold, forming an alloy. Such ores are known
FIG. 23 — Plate of Silver from Confagas Mine Cobalt Dimensions 32X14X1
ins Weight 37 Ibs. (Photo by C W. Knight )
as free milling The silver is freed from the gold and other metals by
a refining process. It is separated from native copper by electrolytic
methods.
Uses — Silver is used in the arts to a very large extent Jewelry,
ornaments, tableware and other domestic utensils, chemical apparatus
and parts of many physical instruments are made of it It is used also
in the production of mirrors and in the manufacture of certain compounds
used in surgery and in photography Its alloy with copper forms the
staple coinage of China, Mexico and most of the South American coun-
tries, and the subsidiary (or small) coinage of most countries In
the United States it is used in the coinage of silver dollars and of frac-
tions of the dollar as small as the dime. The silver corns of the United
States are nine-tenths silver and one-tenth copper, the latter metal being
added to give hardness English corns contain i2| parts silver to one
58 DESCRIPTIVE MINERALOGY
part of copper In 1912 the world's coinage of silver consumed 161,-
763,415 02 , with a value after coinage of $171,293,000
Production —The total production of silver in the United States
during 1912 was over 63,766,000 oz , valued at over $39,197,000, of
which about $100,000 worth came from placers and $325,000 worth
from the copper mines of Michigan The balance was obtained by
smelting silver compounds and in the refining of gold, lead, copper and
zinc ores The world's production of silver during 1912 was 224,488,-
ooo oz , valued at over $136,937,000, but most of this was obtained
from the compounds of silver and not from the native metal The
proportion obtained from the mineral is not definitely known, but the
production of Canada was more than 30,243,000 oz , valued at
$17,672,000 and nearly all of this came from Cobalt, where the ore is
native silver
Gold (Au)
A large portion of the gold of the world has been obtained m the
form of native metal The greater portion of the metal is so very finely
disseminated through other minerals that no sign of its presence can be
detected even with high powers of the microscope Although present
in such minute quantities it is very widely spread, many rocks con-
taining it jn appreciable quantities Its visible grains, as usually found,
are little rounded particles or thin plates or
scales mixed with sand or gravel, or tiny
irregular masses scattered through white vem-
quartz
Native gold rarely occurs in well formed
crystals The metal is so soft that its crystals
are battered and distorted by very slight
pressure. Occasionally well developed crys-
tals, bounded by octahedral, dodecahedral
FIG 24 -Octahedral Skele- and compllcated icositetrahcdral and tetra-
ton Crystal of Gold with ,_,,,- , t
Etched Faces hexahedral faces are met with, but usually
the crystals are elongated or flattened Skele-
ton crystals (Fig. 24) and groups of crystals are more frequently found
than are simple crystals. Twins are common, with O(iii) the twin-
ning plane
As found in nature, gold is frequently alloyed with silver and it
often contains traces of iron and copper and sometimes small quanti-
ties of the rarer metals
Gold containing but a trace of silver up to 1 6 per cent of this metal
INTRODUCTION— THE ELEMENTS 59
is known simply as gold When the percentage of silver present is
larger it is said to be argentiferous When the percentage reaches
20 per cent or above the alloy is called clectru ,: Palladium, rhodium
and bismuth gold are alloys of the last-named metal roth the rare metals
palladium or rhodium or with the more common bismath
The color of the different varieties of the mineral varies from pinkish
silver-white to almost copper-red Pure gold is golden yellow With
increase cf silver it becomes lighter in color and T\ith increase in copper,
darker The rich red-yellow ot much of the gold used in the arts is due
to the admixture ot copper In very thin plates or lea\ es ( ooi mm )
gold is translucent \\ith a blue or green tint
Gold is soft, malleable and ductile Its luster is, of course, metallic
and its streak, yellow When pure its density is 1943, its hardness
between 2 and 3, and its fusing point 1062° The metal is insoluble in
most acids, but it is readily dissolved in a mixture of nitric and hydro-
chloric acids (aqua regia) It is not acted upon by water or the atmos-
phere Its negative properties distinguish it from the other substances
-which it resembles in appearance It is a good conductor of electricity.
Syntheses — Crystals of gold have been obtained by heating a solu-
tion of AuCls in amyl alcohol, and by treating an acid solution of the
same compound with formaldehyde
Occurrence — Native gold is tound in the quartz of veins cutting
through granite and schistose rocks, or in the gravels and sands of rivers
whose channels cut through these, and in the sands of beaches bordering
gold-producing districts It is sometimes found in the compacted
gravels of old river beds, in a rock known as conglomerate, and in sand-
stones It is also present in small quantities in many volcanic rocks,
and is disseminated through pyrite (FeS2) and some other sulphur com-
pounds and their oxidation products
The gold in quartz veins occurs as grains and scales scattered through
quartz irregularly, often in such small particles as to be invisible to the
naked eye, or as aggregates of crystals in cavities in the quartz Pyrite
is nearly always associated with the gold. On surfaces exposed to the
weather the pyrite rusts out and stains the quartz, leaving it cavernous
or cellular
Most of the world's supply of gold has come from placers. These
are accumulations of sand or gravel in the beds of old river courses
The sands of modern streams often contain considerable quantities of
gold Many of the older streams were much larger than the modern
ones draining the same regions and, consequently, their beds contain
more gold This was originally brought down from the mountains or
60 DESCRIPTIVE MINERALOGY
highlands in which the streams had their sources The sands and
gravels were rolled along the streams' bottoms and their greater portion
was swept away by the currents into the lowlands The gold, however,
being much heavier than the sands and pebble grains, merely rolled
along the bottoms, dropping here and there into depressions from which
it could not be removed As the streams contracted in volume the gold
grains were covered by detritus, or perhaps a lava stream flowing along
the old river channel buried them These buried river channels with
their stores of sands, gravels and gold constitute the placers With the
gold are often associated zircon crystals, garnets, diamonds, topazes
and other gem minerals Alluvial gold is usually in flattened scales or
in aggregates of scales forming nuggets Some of the nuggets are so
large, 190 pounds or more in weight, that it is thought they may have
been formed by some process of cementation after they were transported
to their present positions
The gold-quartz veins are usually closely associated with igneous
rocks, but the veins themselves may cut through sedimentary beds or
crystalline schists The veins are supposed to have been filled from
below by ascending solutions Metallic gold is also present m the oxi-
dized zones of many veins of gold-bearing sulphides and m the zones of
secondary enrichment At the surface the iron sulphides are oxidized
into sulphates, leaving part of the gold m the metallic state and dissolv-
ing another part which is carried downward and precipitated
Principal Localities — Vein gold occurs m greater or less quantity in
all districts of crystalline rocks It has been obtained m large quantity
along the eastern flanks of the Ural Mountains, this having been the
most productive region in the world between the years 1819 and 1849
It has been obtained also from the Altai Mountains in Siberia, from the
mountains m southeastern Brazil, from the highlands of many of the
Central and South American countries, and from the western portion of
the United States, more particularly from the western slopes of the Sierra
Nevada Mountains and the higher portions of the Rocky Mountains
In recent years auriferous quartz veins have been worked at various
points m Alaska, at Porcupine, Ontario, and other points in Canada
The great placer mines of the world are in California, Australia and
Alaska In Australia the principal gold mines are situated m the streams
rising in the mountains of New South Wales and their extension into
Victoria The valleys of 'the Yukon and other rivers m Alaska have
lately attracted much attention, and in the past few years the beach
sands off Nome have yielded much of the metal
The most important production at present is from South Africa
INTRODUCTION— THE ELEMENTS 61
where the metal occurs in an old conglomerate In the opinion of some
geologists this is an old beach deposit, in the opinion of others the gold
was introduced into the conglomerate long after it had consolidated
The sands of many streams in Europe and in the eastern United
States have for many years been "panned" or cashed for gold The
South Atlantic States, before the discovery of gold m California, in
1849, yielded annually about a million dollars' worth of the precious
metal All of it was obtained by working the gra\ els and sands of small
rivers and rivulets Many of these streams have been worked o\er
several times at a profit and the mining continues to the present day
Small quantities of gold have also been obtained from streams in Maine,
New Hampshire, Maryland and other Atlantic coast states
Extraction and Refining — Gold is extracted from alluvial sands
and from placers by washing in pans or troughs The sand, gravel
and foreign particles are carried away by currents of water and
the gold settles down with other heavy minerals to the bottom of the
shallow pans used in hand washing, or into compartments prepared for
it in troughs when the processes are on a larger scale It is after-
ward collected by shaking it with mercury or, quicksilver, m \\hich it
dissolves The quicksilver is finally driven off by heat and the gold
left behind Auriferous beach sands and many lake, swamp and mer
sands are dredged, and the sand thus raised is treated by similar methods
Sands containing as low as 15 cents' worth of metal per cubic yard can
be worked profitably under f a\ orable conditions
Where the gold occurs free (not disseminated through sulphides)
in quartz the rock is crushed to a fine pulp -with -water and the mixture
allowed to flow over copper plates coated \uth quicksilver The gold
unites with the quicksilver and forms an alloy from which the mercury
is driven off by heat The process of forming allo}s of silver or gold
with mercury is known as amalgamation
When the gold is disseminated through sulphides, these are concen-
trated, i e , freed from the gangue material by washing and then
roasted This liberates the gold which is collected by amalgamation,
or is dissolved by chlorine or cyanide solutions and then precipitated
Uses — Gold, like silver, is used in the manufacture of jewelry and or-
naments, in the manufacture of gold leaf for gilding and in the produc-
tion of valuable pigments such as the "purple of Cassms " It also con-
stitutes the principle medium for coinage in nearly all of the most
important countries of the world The gold coins of the United States
contain 900 parts gold in 1,000. Those of Great Britain contain 916 66
parts, the remaining parts consisting of copper and silver The total
62 DESCRIPTIVE MINERALOGY
gold coinage of the United States mints from the time of their organi-
zation to the end of the year 1912 amounted to $2,765,900,000 The
gold coined in the world's mints in 1912 amounted m value to $360,-
671,382, and that consumed in arts and industries to $174,100,000
Jewelers estimate the fineness of gold in carats, 24-carat gold being pure
Eighteen-carat gold is gold containing 18 parts of pure gold and 6 parts
of some less valuable metal, usually copper The copper is added to
increase the hardness of the metal and to give it a darker color The
gold used most in jewelry is 14 or 12 carats fine
Production — The total value of the gold product of the United
States during 1912 was $93,451,000 Of this the following states and
territories were the largest producers
Alaska $17,198,000 Nevada $13,576,000
California 20,008,000 South Dakota 7,823,000
Colorado 18,741,000 Utah 4,312,000
Of the total product, placers gelded gold valued at $23,019,633, and
quaitz veins, metal valued at $62,112,000 The balance of the gold was
obtained from ores mined mainly for other metals, and in these it is
probably not in the metallic state Moreover, some of the ore in quartz
veins is a gold telluride, but by far the greater portion of the product
from the quartz veins and placers was furnished by the native metal
The world's yield of the precious metal in 1912 was valued at $466,-
136,100 The principal producing countries and the value of the gold
produced by each were
South Africa $211,850,600 Mexico $24,450,000
United States 93,45 1,500 India 11,055,700
Australasia 54,509,400 Canada 12,648,800
Russia 22,199,000 Japan 4,467,000
Lead occurs very rarely as octahedral or dodecahedral crystals,
in thin plates and as small nodular masses in districts containing man-
ganese and lead ores and also in a few placers It usually contains
small quantities of silver and antimony The native metal ha1} the
same properties as the commercial metal Its hardness 13 i 5 and
density 113 It melts at about 33 5°
The mineral is of no commercial importance The metal is obtained
from galena and other lead compounds
Mercury occurs as small liquid globules in veins of cinnabar (HgS)
from which it has probably been reduced by organic substances, and ift
INTRODUCTION— THE ELEMENTS 63
the rocks traversed by these veins The native metal possesses the
same properties as the commercial metal It solidifies at — 39°, when
it crystallizes in octahedrons ha\mg a cubic cleavage Its density is
13 6 Its boiling-point is 350°
The commercial metal is obtained from cinnabar (p 98).
Amalgam (Ag Hg) is found in dodecahedral crystals in a few places,
associated with mercury and silver ores It occurs also as embedded
grams, m dense masses and as coatings on other minerals It is silver-
white and opaque and gives a distinct silver streak when rubbed on
copper Its hardness is about 3 and its density 13 9 When heated
in the closed tube it yields a sublimate of mercury and a residue of
silver On charcoal the mercury volatilizes, leaving a silver globule,
soluble in nitric acid
PLATINUM-IRON GROUP
The platinum-iron group of minerals may be divided into the plati-
num and the iron subgroups The latter compnses only iron and nickel-
it on, both of which are extremely rare, and the former, the metals
platinum, indium, osmium, ruthenium, rhodium, and palladium The
platinum metals probably constitute an isodimorphous group since
they occur together in alloys, some of which are isometric and others
hexagonal (rhombohedral) Platinum is the only member of the group
of economic importance.
Platinum (Pt)
Platinum occurs but rarely in crystals It is almost universally
found as granular plates associated with gold in the sands of streams
and rivers, and rarely as tiny grains or flakes in certain very basic
igneous rocks
As found in nature the metal always contains iron, indium, rhodium,
palladium and often other metals. A specimen from California yielded:
Pt Au Fe Ir ^Rh Pd Cu IrOs Sand Total
85 50 80 6 75 i 05 i oo 60 i 40 i 10 2 95 101 15
Though the metal occurs usually in grains and plates, nevertheless
its crystals are sometimes found. On them cubic faces are the most
prominent ones, though the octahedrons, the dodecahedrons and
tetrahexahedrons have also been identified Like the crystals of silver
and gold, those of platinum are frequently distorted.
64 DESCRIPTIVE MINERALOGY
The color of platinum is a little more gray than that of silver Its
streak is also gray Its hardness is 4-4 5 and density 14 to 19 Pure
platinum has a density of 21 5 It is malleable and ductile, a good
conductor of electricity, and it is infusible before the blowpipe except
in very fine wire It is not dissoh ed by any single acid, though soluble,
like gold, in aqua regia Its melting temperature is 1755°
Syntheses —Crystals have been obtained by cooling siliceous mag-
mas containing the metal, and by dissolving the metal in saltpelei and
cooling the mixture
Occurrence — Platinum is found in the sands of rivers or beaches
and in placer deposits in which it occurs in flattened scales or in
small grains Nuggets of considerable size are sometimes met with,
the largest known weighing about iSf kilos It is present also in
small quantity in certain very basic igneous rocks, like pendotite
Localities — It occurs m nearly all auriferous placer districts and
in small quantities in the sands of many rivers, among them the Ivalo
in Lapland, the Rhine, the rivers of British Columbia, and of the Pacific
States It is more abundant in the Natoos Mountains in Borneo, on
the east flanks of the Ural Mountains in Siberia, in the placer of an
old river in New South Wales, Australia, and the sands of rivers of
the Pacific side of Colombia It is nearly always associated with
chromite (p 200) A recent discovery which may prove to be of con-
siderable importance is near Goodsprmgs, Nev , where platinum is in
the free state associated with gold in a siliceous oie
The native metal is probably an original constituent of some pen-
dotites (basic igneous rocks) Its presence m placers is due to the
disintegration of these rocks by atmospheric agencies
Extraction and Refimng — The metal is separated from the sand
with which it is mixed by washing and hand picking The metallic
powder is then refined by chemical methods
Uses — On account of its infusibihty and its power to resist the coi-
rosion of most chemicals the metal is used extensively for ciuciblcs
and other apparatus necessary to the work of the chemist It is also
used by dentists and by the manufacturers of incandescent electric
lamps It is an important metal in the manufactuie of physical and
certain surgical instruments, and was formerly used by Russia for coin-
age The most important use of the metal in the industries is in the
manufacture of sulphuric acid Sulphur dioxide (SCb) and steam when
mixed and passed over the finely divided metal unite and foim HjSOi
More than half of the acid made at present as manufactured by this
process
INTRODUCTION— THE ELEMENTS
65
Production — Most of the platinum of the world is obtained from
placers in the Urals in Russia A small quantity is washed from the
sands of gold placers in Colombia, Oregon and California, and an even
smaller quantity is obtained during the refining of copper from the ores
of certam mines The total production of the world in 1912 was
314,751 oz The output for Russia m this year was about 300,000 oz ,
of Colombia about 12,000 oz , and of the United States 721 oz (equiv-
alent to 505 02 of the refined metal, valued at $22,750) In addition,
about 1,300 oz were obtained m the refining of copper bullion imported
from Sudbury, Ont , and m the treatment of concentrates from the
New Rambler Mine, Wyoming Of this about 500 oz were produced
pIG 35 — iron Meteorite (Sidente) from Canyon Diablo, Arizona Weight 265
Ibs (Field Columbian Museum )
from domestic ores The importations into the United States for the
same year were about 125,000 oz , valued at $4,500,000
Platinum-iron, or iron-platinum (Pt Fe), contains from 10 per cent
to 19 per cent Fe It is usually dark gray or black and is magnetic It
is found with platinum m sands of the rivers in the Urals Its crystals
are isometric
Iron (Fe) occurs in small grains and large masses in the basalt at
Ovifak, Disko Island, W Greenland, and at a few other points in Green-
land, and alloys consisting mainly of iron are found in the sands of some
rivers in New Zealand, Oregon and elsewhere The native metal always
contains some nickel The most common occurrence of iron, however, is
m meteorites (Fig 25) In these bodies also it is aUoyed with Ni When
66
DESCRIPTIVE MINERALOGY
polished and treated with nitric acid, surfaces of meteoric iron exhibit
penes of lines (Widmanstatten figures), that are the edges of plates of
different composition (Fig 26) These are so arranged as to indicate
that the substance crystallizes in the isometric system
Iridium (Ir Pt) and platin-iridium (Pt Ir) are alloys of indium and
platinum found as silver- white grains with a yellowish tinge, associated
with platinum in the sands of rivers in the Urals, Burmah and Brazil
Their hardness is 6 to 7, and density 22 7 The mineral is isometric
and its fusing point is between 2i5o°-225o°.
FIG 26 — Widmanstatten Figures on Etched Surface of Meteorite from Toluca,
Mexico (One-half natural size ) (Field Columbian Mit\cntn )
Palladium (Pd) is usually alloyed with a little Pb and Ir It is
found in small octahedrons and cubes and also in radially fibrous grams
in the platinum sands of Brazil, the Urals and a few other places It is
whitish steel-gray in color, has a hardness of 4 to 5 and a density of
ii 3 to ii 8 It fuses at about 1549° Its crystallization is isometric
About 2,390 oz of the metal were produced in the United States during
1912, but all of it was obtained during the refining of bullion. The
imports were 4,967 oz , valued at $213,397
Allopalladium (Pd) is probably a dimorph of palladium It is found
in six-sided plates that are probably rhombohedral, intimately asso-
ciated with gold, at Tilkerode, Harz
INTRODUCTION— THE ELEMENTS 67
Osmiridium (Os Ir) and mdosmine (Ir Os) are foundm crystals and
flattened grams and plates that are apparently rhombohedral They
consist of Ir and Os m different proportions, often with the addition
of rhodium and ruthenium Osmiridium is tin-white and iridosrmne
steel-gray Their hardness is 6 to 7 and density 19 to 21 When heated
with KNOs and KOH, both yield the distinctive chlorine-like odor of
osmium o\ide (Os04) and a green mass, \\hich, when boiled with
water, leaves a residue of blue indium oxide Both are insoluble in
concentrated aqua regia They occur \\ith platinum in the sands of
rivers m Colombia, Brazil, California, the Urals, Borneo, New South
Wales, and a few other places They are distinguished from platinum
by greater hardness, light color and insolubility in strong aqua regia
The world's product of refined indium is about 5,000 oz , of which
the United States furnishes about 500 oz Its value is $63 per oz
Imports into the United States during 1911 were 3,905 oz, valued at
$210,616 The sources of the metal are native indium, osrniridmm,
platinum, copper ore and bullion The metal is obtained from the last
two sources in the refining process
CHAPTER IV
THE SULPHIDES, TELLURIDES, SELENIDES, ARSENIDES AND
ANTIMONIDES
THE sulphides are combinations of the metals, or of elements acting
like bases, with sulphur They may all be regarded as derivatives of
hydrogen sulphide (H2S) by the replacement of the hydrogen by some
metallic element The tellundes are the corresponding compounds of
EfeTe, and the selemdes of EkSe
With the same group are also placed the arsenides and the anti-
monides, derivatives of HsAs and HsSb, because arsenic and antimony
so often replace m part the sulphur of the sulphides, forming with these
isomorphous mixtures
The minerals described in this volume may be separated into the
following groups and subgroups
I The sulphides, tellundes and selemdes of the metalloids arsenic,
antimony, bismuth and molybdenum
II The sulphides, tellundes, selemdes, arsenides and antimonides
of the metals
(a) The monosulphides, etc (Derivatives of HsS, HgSe, HsTe,
H3As, H3Sb )
(&) The disulphides, etc (Derivatives of 2HsS, 2H2Te, 2HsAs,
2H3Sb)
All sulphur compounds when mixed with dry sodium carbonate
(Na2COs) and heated to fusion on charcoal yield a mass containing
sodium sulphide (Na2$) If the mass is removed from the charcoal,
placed on a bright piece of silver and moistened with a drop or two of
water or hydrochloric acid, the solution formed will stain the silver a
dark brown or black color (AgsS), which will not rub off The sulphides
yield the sulphur reaction when heated with the carbonate on platinum
foil, the sulphates only when charcoal or some other reducing agent is
added to the mixture before fusing Moreover, the sulphides yield
sulphureted hydrogen when heated with hydrochloric acid, while the
sulphates do not. These tests are extremely delicate. By the aid of
SULPHIDES, TELLURIDES, ETC 69
the first one the sulphur in any compound may be detected By the
aid of the others the sulphates may be distinguished from the
sulphides
The selemdes are recognized by the strong odor evolved \\hen heated
before the blowpipe Selenates and selemtes give their odor only after
reduction with Na2COs
The tellundes, \\hen wanned with concentrated HoSO-t, dissolve and
yield a carmine solution from which water precipitates a black gray
powder of tellurium
All substances containing arsenic and antimony yield dense white
fumes when heated on charcoal in the oxidizing flame The fumes of
arsenic possess a characteristic odor while those of antimony are odorless
When heated in the open tube, arsenides and compounds \\ith sulphur
and arsenic yield a very volatile sublimate composed of tiny white crys-
tals (AS203) The corresponding sublimate for antimomdes and for
compounds with antimony and sulphur is nonvolatile, or difficultly
volatile, and apparently amorphous It is usually found on the under
side of the tube
THE SULPHIDES, SELENIDES AND TELLURIDES OF
THE METALLOIDS
The sulphides of the metalloids include compounds of sulphur with
arsenic, antimony, bismuth and molybdenum and a selemde and several
tellundes of bismuth Only the sulphides are of importance. One,
shbmte (Sb2Ss), is utilized as a source of antimony
Realgar (As2S2)
Realgar occurs as a bright red incrustation on other substances,
as compact and granular masses and as crystals implanted on other
minerals It is usually associated with the bright yellow orpunent
(P 7i)
Absolutely pure realgar should have the following composition
As, 70 i per cent, S, 29 9 per cent The mineral, however, usually
contains a small amount of impurities It may be looked upon as a
derivative of H2S in which the hydrogen of two molecules is replaced
by two arsenic atoms, thus*
H2S As=S
yielding |
H2S As=S,
70
DESCRIPTIVE MINERALOGY
oo P 5b , oio (b) , oP, ooi
(c), Poo, on (q) and P,
in M
Crystals of realgar are usually short and prismatic m habit They
are monoclmic (prismatic class) with an axial ratio a b c =i 44
i . 973 and /3=66° 5' The characteristic prismatic faces are
(w)ooP(uo) and (J)ooP2(2io) These with (b) oo P 5b (oio) con-
stitute the prismatic zone The terminations are (r) \? 00(012) or
(q) Pob (on) in combination with the basal plane (0 oP(ooi), the
orthodome (a) (Toi), and one or more of several pyramids (See Fig
27 ) The crystals are usually small and are
striated vertically Prismatic angle 1 10 A ilo
= 105° 34'
The mineral possesses a distinct cleavage
parallel to (fc)ooPoo and (/) oo P5 It is
sectile, soft (H= i 5-2), resinous in luster and
aurora-red or orange in color Its streak is a
lighter shade, but with the mineral are fre-
quently intermingled small quantities of orpi-
FIG 27 — Realgar Crystal ment which impart to its streak a distinct
yellow tinge Its density is 3 56 In thin
splinters it is often translucent or trans-
parent, and strongly pleochroic m red and
yellow tints, but in masses it is opaque Its
indices of refraction are not known with accuracy, but its double re-
fraction is strong ( 030) It is a nonconductor of electricity
When heated on charcoal before the blowpipe realgar catches fire
and burns with a light blue flame, at the same time giving off dense
clouds of arsenic fumes and the odor of burning sulphur (SOs) When
heated in a closed tube it melts, volatilizes and yields a transparent
red sublimate in the cold parts of the tube
Its bright red color and its reaction for sulphur distinguish realgar
from all other minerals but cinnalar, the sulphide of mercury (p 9#)
It may easily be distinguished from cinnabar by its softness, its low
specific gravity and the arsenic fumes which it yields when heated on
charcoal
On exposure to the air and to light realgar oxidizes, yielding orpi-
ment (As2Ss) and arsenolite (As20s)
Syntheses —Realgar is often produced in the flues of furnaces m
which ores containing sulphur and arsenic are roasted Crystals have
also been produced by heating to 150° a mixture of AsS with an excess
of sulphur in a solution of bicarbonate of soda sealed m a glass tube
Occurrence Localities and Origin — Realgar occurs in masses asso
dated with orpiment and m grams scattered through it at all places
SULPHIDES, TELLURIDES, ETC 71
where the latter mineral is found It also occurs associated with silver
and lead ores in many places It is found in crystals implanted on
quartz and on the walls of cavities in lavas It "is also occasionally
a deposit from hot springs In the United States it forms seams in a
sandy clay in Iron Co , Utah Its crystals are found in calcite in San
Bernardino and Trinity Counties, California, and with orpiment it is
deposited as a powder by the hot water of the Norns Geyser basin in the
Yellowstone National Park
In most cases it is a product of the interaction of arsenic and sul-
phur vapors.
Uses — The native realgar occurs in too small a quantity to be of
commercial importance An artificial realgar is employed in tanning
and m the manufacture of " white-fire "
Orpiment (As2S3)
Orpiment, though more abundant than realgar, is not a common
mineral It is usually found m foliated or columnar masses with a.
bright yellow color Its name — a contraction from the Latin aun-
pigmentum, meaning golden paint — refers to this color
The pure mineral contains 39 per cent of sulphur and 61 per cent
of arsenic, corresponding to the formula As2Sa It thus contains
about 9 per cent more sulphur than does realgar.
The monoclmic orpiment crystals have the symmetry of the pris-
matic class Their axial ratio is 596 . i * 665 with £=89° 19' Though
always small they are distinctly prismatic with an orthorhombic habit
Their predominant faces are the ortho and clino pmacoids, several
prisms and the orthodome
The cleavage of orpiment is so perfect parallel to °o P ob (oio) that
even from large masses of the mineral distinct foliae may be split
These are flexible but not elastic The mineral, like many other
flexible minerals, is sectile Its luster is pearly on cleavage faces,
which are always vertically striated, and is resinous on other surfaces
The color of pure orpiment is lemon-yellow, it shades into orange
when the mineral is impure through the admixture of realgar Its
streak is always of some lighter shade than that of the mineral Its
hardness is i 5-2 and its density about 34 In small pieces orpiment
is translucent and possesses an orange and greenish yellow pleochroism
When heated to 100° it becomes red and assumes the pleochroism of
realgar. It, however, resumes its characteristic color and pleochroism
upon cooling. When heated to 150° the change is permanent. The
mineral is a nonconductor of electricity.
72 DESCRIPTIVE MINERALOGY
The chemical properties of orpiment are the same as those described
for realgar, except that the sublimate in the closed tube is yellow instead
of red
Synthesis —Orpiment is produced in large plcochroic crystals by
treatment of arsenic acid with H2S under high prcssuie
Occurrence, Localities and Origin —Orpiment occurs in the same
forms and in the same places as does realgar Small specks of it occur
on arsenical iron at Edenville, NY It is also found in the deposits
of Steamboat Springs Nevada The origin of orpiment is similar
to that of realgar It is also formed by the oxidation of this mineral
Uses —Native orpiment mixed with water and slaked lime is used
in the East as a wash for removing hair It is also employed as a pig-
ment in dyeing Most of the As2§3 of commerce is a manufactured
product
STIBNITE GROUP (R>Q3)
The stibmte group of sulphides contains several isomorphous
compounds, of which we shall consider only two, viz , Uibmtc
and Usmuthimte (61283) The general formula of the group is
m which R stands for Sb or Bi and Q for S 01 Se The gioup is
orthorhombic (bipyramidal class) All the members have a distinct
cleavage parallel to the brachypmacoid which yields flexible laminae
Sfobnite (Sb2Sa)
Stibmte is the commonest and the most important ore of anti-
mony It is found in acicular and prismatic crys-
tals, in radiating groups of crystals and m
fibrous masses
Chemically, stibmte is the antimony tnsul-
phide, SboSa, composed of SI), 71 4 per cent
and S, 28 6 per cent Ab found, however, it
usually contains small quantities of iron and often
traces of silver and gold
„ „ „ , ^ Crystals of stibmte are often very comnh-
FIG 28 —Stibmte Crys- , , «,, 11, i .
tal M p no (w) ca^ec^ They are orthorhombic with an axial ratio
OOP So, oio (ft), 2P2^ 9926 * i 10179 and a columnar or acicular
121 00 and P, iii(.p) habit The most important forms m the pris-
matic zone are oo P(no) and oo P 56 (oio). The
prisms are often acutely terminated by P(iu), ^4(431) and 6P2»(36i),
or bluntly terminated by iP(ii3), (Fig 28) Sometimes the crystals
are rendered very complicated by the great number of their terminal
SULPHIDES, TELLURIDES, ETC. 73
planes Dana figures a crystal from Japan that possesses a termina-
tion of 84 planes no A ilo=89° 34'
Many of the crystals of this mineral, more particularly those with
an acicular habit, are curved, bent or twisted Nearly "all, whether
curved or straight, are longitudinally striated
The cleavage of stibmte is very perfect parallel to oo P 06 (oio),
leaving striated surfaces The mineral is soft (H=2) and slightly
sectile Its density is about 4 5 Its color is lead-gray and its streak
a little darker In very thin splinters it is translucent in red or yellow
tints In these the indices of refraction for yellow light have been
determined to be, 0^=4303 and 7=3 194 Surfaces that are exposed
to the air are often coated with a black or an iridescent tarnish The
luster of the mineral is metallic It is a nonconductor of electricity
Stibmte fuses very easily, thin splinters being melted even in the
flame of a candle When heated on charcoal the mineral yields anti-
mony and sulphurous fumes, the former of which coat the charcoal white
in the vicinity of the assay When heated in the open tube SCb is
evolved and a white sublimate of Sb20s is deposited on the cool walls of
the tube In the closed tube the mineral gives a faint ring of sulphur
and a red coating of antimony oxysulphide It is soluble in nitric acid
with the precipitation of Sb20s
Stibmte may easily be distinguished from all minerals but the other
sulphides by the test for sulphur From the other sulphides it is dis-
tinguished by its cleavage and the fumes it yields when heated on char-
coal Its closest resemblance is with galena (PbS), which, however,
differs from it in being less fusible and in yielding a lead globule when
fused with sodium carbonate on charcoal. Moreover, galena possesses
a cubic cleavage
Syntheses — Stibnite is produced by heating to 200°, a mixture of
sulphur and antimony with water under pressure, and by the reaction of
H2S on antimony oxide heated to redness
Occurrence, Localities and Origin — The mineral is found as crystals
in quartz veins cutting crystalline rocks, and in metalliferous veins asso-
ciated with lead and zinc ores, with cinnabar (HgS) and barite (BaSO-i)
The finest crystals, some of them 20 inches in length, come from mines
in the Province of lyo, on the Island of Shikoku/Japan The mineral
occurs also m York Co , New Brunswick, in Rawdon township, Nova
Scotia, at many points in the eastern United States, in Sevier Co ,
Arkansas, in Garfield Co , Utah, and at many of the mining districts in
the Rocky Mountain States
In Arkansas stibmte is in quartz veins following the bedding planes
74 DESCRIPTIVE MINERALOGY
of shales and sandstones With it are found many lead, zmc and
iron compounds and small quantities of rarer substances In Utah
the mineral occurs m veins unmixed AMth other minerals, except its
o\\n oxidation products The veins follow the bedding of sandstones
and conglomerates Here, as in Arkansas, the stibnite is believed to
have been deposited by magmatic waters
Uses —Stibnite was powdered by the ancients and used to color the
eyebrows, eyelashes and hair At present it is used to a slight extent in
vulcanizing rubber and in the manufacture of safety matches, percussion
caps, certain kinds of fireworks, etc Its principal value is as an ore of
antimony Practically all of the metal used in the arts is obtained
from this source Antimony is chiefly valuable as an alloy with other
metals With tin and lead it forms type metal The principal alloys
with tin are britannia metal and pewter With lead, tin and copper
it constitutes babbit metal, a hard alloy used in the construction of
locomotive and car journals, and with other substances it enters into
the composition of other alloys used for a variety of purposes The
double tartrate of antimony and potassium is the well known tartar
emetic. The pigment, Naples yellow, is an antimony chromate.
Production — The total quantity of stibnite mined in the world can-
not be accurately estimated That mined in the United States is very
small in amount, most of the antimony produced m this country being
obtained in the form of an antimony alloy as a by-product in the smelting
of antunomal lead ores
Bismuthinite (Bi2S3)
Bismuthimte is completely isomorphous with stibnite It rarely,
however, occurs in acicular crystals, but is more frequently in foliated,
fibrous or dense masses
Its axial ratio is 968 i : 985.
The angle noAiTo = 88° 8'
The mineral resembles stibnite in color and streak, but its surface is
often covered with a yellowish iridescent tarnish Its fusibility and
hardness are the same as those of stibnite but its density is 6 8-7 i It
is an electrical conductor
In the open tube the mineral yields S02 and a white sublimate
which melts into drops that are brown while hot, but change to opaque
yellow when cold On charcoal it yields a coating of yellow 81203 which
changes to a bright red Bils when moistened with potassium iodide
The mineral dissolves in hot nitric acid, forming a solution, which upon
the addition of water gives a white precipitate of a basic bismuth nitrate.
SULPHIDES, TELLURIDES, ETC ?5
Bismuthmite is distinguished from stibmte by the coating on char-
coal and by its complete solubility in HNOa
Syntheses — Crystals have been obtained by cooling a solution of
m molten bismuth, and by cooling a solu.ion made by heating
BioSs m a solution of potassium sulphide in a closed tube at 200°.
Occurrence , Localities and Origin — Bismuthmite occurs as a constit-
uent of veins associated \vith quartz, bismuth and chalcopynte, in which
it was probably formed as a product of pneumatolytic processes It is
found at Schneeberg and other points in Saxony, at Redruth and
elsewhere in Cornwall, near Beaver City, Utah, in a gold-bearing veiii
at Gold Hill, Rowan County, N C , and in a vein containing benl,
garnet, etc , in granite at Haddam, Conn
TETRADYMITE GROUP
This group comprises a series of tellundes and selemdes of bismuth
that have not been satisfactorily differentiated because of the lack of
accurate analyses
Tetradymite, the best known member of the group, is probably an
isomorphous mixture cf bismuth tellunde and bismuth sulphide of the
formula Bi2(Te 8)3 It occurs in small rhombohedral cnstals with the
axial ratio i . i 587 and loli A 1101 = 98° 58' Its crystals are bounded
by rhombohedrons (R(ioTi) and 2R(202ii)) and the basal plane
(oP(oooi)). Interpenetration fourlings are common with — |R(oil2),
the twinning plane The mineral is, however, more frequently found
in foliated and granular masses. Its color is lead-gray It possesses a
perfect cleavage parallel to the base Its hardness is i 5-2 and its
density about 74 It is a good electncal conductor Its best known
occurrences are Zsubkau, Hungary, Whitehall, Va, in Davidson
County, N C , near Dahlonega, Ga , near Highland, Mont , and at
the Montgomery Mine and at Bradshaw City in Arizona It occurs in
quartz veins associated with gold in the gold sands of some streams
The other members of the group appear to be completely isomorphous
with tetradymite. They vary m color from tin-white through gray to
black.
Molybdenite (MoS)
This mineral, which is the sulphide of the rare metal molybdenum,
does not occur in large quantity, but it is so widely distributed that it
seems to be quite abundant It occurs principally in black scales scat-
76 DESCRIPTIVE MINERALOGY
tered through coarse-grained, crystalline, siliceous rocks and granular
limestones and in black or lead-gray foliated masses
The theoretical composition of molybdenite is 40 per cent sulphur
and 60 per cent molybdenum Usually, however, the mineral contains
small quantities of iron and occasionally other components
Crystals of molybdenite are exceedingly rare Scales and plates
with hexagonal outlines are often met with but they do not usually pos-
sess sufficiently perfect faces to >ield accurate measurements The
measurements that have been obtained appear to indicate a holohedral
hexagonal symmetry with an axial ratio i i 908
The cleavage of molybdenite is very perfect parallel to the base.
The laminae are flexible but not elastic The mineral is sectile and so
soft that it leaves a black mark when drawn across paper Its density
is 4 7. Its luster is metallic, color lead-black, and streak greenish
black In very thm flakes the mineral is translucent with a green tinge
Otherwise it is opaque It is a poor conductor of electricity at ordi-
nary temperature, but its conductivity increases with the temperature
In the blowpipe flame molybdenite is infusible It, however, im-
parts to the edges of the flame a yellowish green color Naturally, it
yields all the reactions for sulphur, and in the open tube it deposits a
pale yellow crystalline sublimate of MoOs Molybdenite is decomposed
by nitric acid with the production of a gray powder (MoOs)
By its color, luster and softness molybdenite is easily distinguished
from all minerals but graphite From this it is distinguished by its
reaction for sulphur Moreover, a characteristic test foi all molyb-
denum compounds is the dark blue coating produced on porcelain when
the pulverized substance is moistened with concentrated sulphuric
acid and then heated until almost dry Before this test can be applied
to molybdenite, the mineral must first be powdered and then oxi-
dized by roasting in the air for a few minutes or by boiling to dryness
with a few drops of HNOs
Syntheses —Crystalline molybdenite has been prepared by the action
of sulphur vapor or EfeS upon glowing molybdic acid It has also been
produced by heating a mixture of molybdates and lime, in a large excess
of a gaseous mixture of HC1 and EfeS.
Occurrence, Localities arid Origin — Molybdenite generally occurs
^embedded as grams in limestone and in the crystalline silicate rocks,
as, for instance, granite and gneiss, and as masses in quartz veins, at
Arendal, Norway, at Blue Hill Bay, Maine, at Haddam, Conn , m
Renfrew Co , Ontario, and at many points in the far western states
It is thought to be of pneumatolytic origin.
SULPHIDES, TELLURIDES, ETC 77
Uses — The mineral is the principal ore of the metal molybdenum,
the salts of which are important chemicals employed principally in
analytical work, especially in the detection and estimation of phosphoric
acid The mol^bdate of ammonia (NH^MoO^ the principal salt
employed in analytical processes, is easily obtained by roasting a mix-
ture of sand and molybdenite and treating the oxidized product with
ammonia Other molybdenum salts are used for giving a green color
to porcelain The metal is used in an alloy (ferro-mol}bdenum) for
hardening steel, as supports for the lower ends of tungsten filaments in
electric lamps and for making ribbons used in electric furnaces
Production — There was no production of molybdenite in North
America during 1912 The imports of the metal into the United States
aggregated 3 5 tons, valued at $4,670. The value of the imports
of the ore is not known*
THE SULPHIDES, SELEWIDES, ETC., OF THE METALS
THE METALLIC MONOSULPHIDES, ETC
The metallic monosulphides, monoselemdes, etc , are compounds
in which the hydrogen of H2S, H2Se, H2Te, HsAs, and HsSb are
replaced by metals Among them are some of the most important
ores
They may be separated into several groups of which some are
among the best defined of all the mineral groups, while others consist
simply of a number of minerals placed together solely for convenience
of description In addition, there are a few members of this chemical
group which seem to have no close relationship with any other mem-
bers These are discussed separately
The groups described are as follows:
The Dyskrasite Group
The Galena Group
The Chalcocite Group.
The Blende Group
The Millerite Group
The Cinnabar Group.
DYSKRASITE GROtJP
This group includes a number of arsenides and antimonides, some
of which apparently contain an excess of the metal above that neces-
sary to satisfy the formulas HsAs and HsSb. Although their com-
78 DESCRIPTIVE MINERALOGY
position is not understood, they are generally regarded as basic com-
pounds A few of them are well crystallized, but their composition is
doubtful, because of the difficulty of obtaining pure material for anal-
yses Some of them are probably mixtures The members of the
group, all of which are ccmparatrvely rare, are wkitneyite (CuoAs),
algodomte (CueAs), domeykite (CuaAs), horsfordite (Cu^Sb) and dyskras-
ite (AgaSb) Other minerals are known which may properly be placed
here, but their identity is doubtful The only two members that need
further discussion are domeykite and dyskrasite
Domeykite (CuaAs) is known only in disseminated particles and
in botryoidal and dense masses and small orthorhombic crystals It
may be a mixture of several components, which in other proportions
form algodomte It is tin-white or steel-gray and opaque It becomes
dull and covered with a yellow or brown iridescent tarnish when ex-
posed to the air Its hardness is 3-4 and density about 73 It is the
most easily fusible of the copper arsenides Its principal occurrences
are m the silver mines of Copiapo and Coquimbo in Chile, associated
T\ith native copper at Cerro de Paracabas, Guerrero, Mexico, at Shel-
don, Portage Lake, Michigan, and on Michipicoten Island, in Lake
Superior, Ontario The last two occurrences are in quartz veins
Dyskrasite (AgaSb) occurs in foliated, granular and structureless
masses and rarely in small orthorhombic crystals with an hexagonal
habit Their axial ratio is 5775 i . 6718, Twinning is frequent,
yielding star-shaped aggregates The mineral has a silver-white color
and streak, but its exposed surfaces are often tarnished yellow or bUck
It is opaque and sectile Its hardness is 3 5-4 and density about 9 6
It is a good electrical conductor Dyskrasite is soluble in HNO^
leaving a white sediment of Sb20s It occurs principally in the silver
mines of central Europe, and especially near Wolfach, Baden, St
Andreasberg, Harz, and at Carnzo, in Copiapo, Chile.
GALENA GROUP
The minerals comprising the galena group number about a dozen
crystallizing m the holohedral division of the regular system (hex-
octahedral class) They possess the general formula RQ in which
R represents silver, lead, copper and gold, and Q sulphur, selenium
and tellurium The group may be divided into silver compounds and
lead compounds, thus (A) argentite (Ag2S), hessite (Ag2Te), petzite
((Ag Au)2Te), naumanmte (Ag2Se), agmlante (Ag2(Se S)), jalpaitc
SULPHIDES, TELLURIDES, ETC 79
((Ag Cu)2S) and eukante ((Ag Cu)2Se), and (B) galena (PbS\ altaite
(PbTe), and dausttalite (PbSe) Of these onh two are of importance,
viz, galena, and argentite Hessite and petzite are comparative!}
unimportant ores of gold
Argentite (AgoS)
Argentite, though not very widespread m its occurrence, is an
important ore of silver It is found in masses, as coatings, and in crys-
tals or arborescent groups of crystals
Argentite contains 87 i per cent silver and 12 9 per cent sulphur when
pure It is usually, however, impure through the admixture of small
quantities of Fe, Pb, Cu, etc
The forms most frequently observed on argentite crystals are
ooOoo(ioo), ooO(no) and 0(in), though various wOoo (hid) and
wOm (hll) forms are also met Tvith The crystals are often distorted
and often they are grouped in paiallel growths of different shapes
Twinning is common, with 0(in) the twinning plane The twins
are usually penetration twins The habit of most crystals is cubical
or octahedral
Argentite is lead-gray in color Its streak is a little darker The
mineral is opaque Its luster is metallic, its hardness about 2 25 and*
density 73 It is sectile, has an imperfect cleavage and is a conductor
of electricity
When heated on charcoal argentite shells and fuses, yielding sulphur
fumes and a globule of silver It is soluble m nitric acid
Argentite is easily recognized by its color, its sectility, the fact that
it yields a silver globule when fused with Na2COs on charcoal and yields
the sulphur test with a silver corn
Syntheses — Crystals of argentite may be obtained by treating red
hot silver with sulphur vapor or dry HfcS, and by heating silver and SCb
in a closed tube at 200°
Occurrence, Localities and Origin — The mineral is found in the second-
ary enrichment zones of veins associated with silver and other sulphides
in many silver-mining districts In Nevada it is an important ore at
the Comstock lode and in the Cortez district It is found also near
Port Arthur on the north shore of Lake Superior, in Ontario, and asso-
ciated with native silver in the copper mines of Michigan The ores of
Mexico, Chile, Bolivia and Peru are composed largely of this mineral.
Production — Much of the silver produced in this country is obtained
from argentite, though by no means so great a quantity as is obtained
from other sources*
80 DESCRIPTIVE MINERALOGY
Hessite (Ag2Te) and Petzite ((Ag Au)2Te)
These two minerals, though comparatively rare, are prominent
sources of gold and silver in some mining camps They usually occur
together associated with other sulphides.
Hessite is the nearly pure silver tellunde and petzittf, &n isomorphous
mixture of gold and silver tellundes, as indicated by the following analy-
ses of materials from the Red Cloud Mine, Boulder Co , Colorado
Te
Ag
Au Cu
Pb Fe
Zn
Si02
Total
I
3786
59 9i
22 17
45 i 35
99 96
II
34 9i
50 66
13 09 °7
17 36
IS
70
100 01
III
32 97
40 80
24 69
i 28
21
05
100 00
The minerals crystallize in all respects like argentite They are
opaque and lead-gray to iron-black in color, sectile to brittle, have a
hardness between 2 and 3 and a specific gravity of 8 3-9, increasing with
the percentage of gold present They are good conductors of electricity
Before the blowpipe, both minerals melt easily to a black globule, at
the same time coloring the reducing flame greenish and giving the odor
of tellurium fumes When acted upon by the reducing flame, the globule
becomes covered with little crystals of silver With Na2COs on charcoal
both minerals yield a globule of silver, but the globule obtained from
hessite dissolves in warm HNOs, while that obtained from petzite
becomes yellow (gold) In the open tube both yield a white sublimate
of TeO2 which melts, when heated, to colorless drops When heated
with concentrated H^SCU, they give a purple or red solution which, upon
the addition of water, loses its color and precipitates blackish gray,
powdery tellurium. The minerals dissolve in HNOs From this solu-
tion HC1 throws down white silver chloride
Both the minerals resemble very closely many forms of argentite
and galena, from which, however, they may be distinguished by the
reactions for tellurium Petzite and hessite may be distinguished from
one another by the test for gold Moreover a fresh surface of hessite
blackens when treated with a solution of KCN, whereas a surface of
petzite remains unaffected
Syntheses —Octahedrons of hessite are obtained by the action of
tellurium vapor upon glowing silver in an atmosphere of nitrogen, and
dodecahedrons of petzite upon similar treatment of gold-silver alloy
Origin — Both minerals are believed to be primary deposits orig-
inating in magmatic solutions They occur in veins with native gold,
quartz, fluonte, dolomite, and various sulphides and other tellundes.
SULPHIDES, TELLURIDES, ETC 81
Localities —These tellundes, together uith others to be described
later (p 113), are important sources of silver and gold in the mines at
Nagyag, Transylvania, at Cripple Creek and in Boulder Co , Colo , and
at Kalgoorhe, W Australia The quantity of tellundes mined is con-
siderable, but since it is impracticable to separate these t\\o tellundes
from the other compounds of gold and silver mined with them, it is im-
possible to estimate the proportion of the metals obtained from them
Galena (PbS)
Galena, the most important ore of lead, occurs in great lead-gray
crystalline masses, in large and small crystals, in coarse and fine granukr
aggregates, and in other less common forms Much galena contains
silver, m which case it becomes an important ore of this metal
Galena rarely approaches the theoretical composition 13 4 per cent
cf sulphur and 86 6 per cent of lead It usually contains small quanti-
ties of the sulphides cf silver, zinc, cadmium, copper and bismuth and
in some cases native silver and gold When the percentage of silver
present reaches 3 oz per ton the mineral is ranked as a silver ore This
silver is apparently present in some cases as an isomorphous mixture
of silver sulphide and m other cases in distinct
minerals included within the galena
Galena crystals usually possess a cubical habit,
though crystals with the octahedral habit are
very common The principal forms observed are
ooOoo(ioo), 0(in), ooO(no), mQoo(klo) and
mQm (hlT) (Figs 29 and 30) Twins are common,
\\ith 0 the twinning face FlG 29 -Galena ays-
Galena is well characterized by its lead-gray * * °°' J,°?
color, its perfect cleavage parallel to the cubic faces an^ Q, ni (o)
and by its great density (8 5) Its luster is me-
tallic and its hardness about 2 6 Its streak is grayish black. It is a
good conductor of electricity
On charcoal galena fuses, yielding sulphurous fumes and a globule
of metallic lead, which may easily be distinguished from a silver globule
by its softness The charcoal around the assay is coated with a yellow
sublimate of lead oxide (PbO) The mineral is soluble in HNOs with
the separation of sulphur
Its color and luster distinguish galena from nearly all minerals but
s Unite From this mineral it is easily distinguished by its more difficult
fusibility, by its cleavage, and by the fact that it does not yield the anti-
mony fumes when heated on charcoal
82
DESCRIPTIVE MINERALOGY
Galena weathers readily to the sulphate (anglesite) and carbonate
(cerussite) , consequently it is usually not found m the upper portions
of veins that are exposed to the action of the air.
Syntheses —Crystals of galena result from heating a mixture of
lead oxide with NEUCl and sulphur, and from treatment of a lead salt
with HgS at a red heat Small crystals have been produced by heating
FIG 30 — Galena Crystals (<*>OQ°(IOO) and O(in)) partly covered by Manasitc,
from the Joplm District, Mo (After UT 6 T Smith and C I1 bitbentlial )
in a sealed glass tube at 8o°-9o° pulverized cerussite (PbCO,j) in a water
solution of HkS
Origin — Veins of galena containing silver (silver-lead) were probably
produced by ascending solutions emanating from bodies of igneous
rocks, while the galena in limestone was probably deposited by ground-
water that dissolved the sulphide from the surrounding sedimentary
rocks Galena is also in some cases a metamorphic product
Occurrence — The mineral occurs very widely spread It is found
in veins associated with quartz (SiCfe), calcite (CaCOa), bante (BaSOi)
or fluonte (CaF2) and various sulphides, especially the zinc sulphide,
sphalerite, in irregular masses filling clefts and cavities in limestone,
SULPHIDES, TELLURIDES, ETC 83
in beds, and in stalactites and other forms characteristic of water
deposits
It occurs also as pseudomorphs after pyromorphite— the lead phos-
phate The form that occurs in veins is often silver bearing, while that
in limestone is usually free from silver
Localities — Galena is mined m Cornwall and in Derbyshire, Eng-
land, in the Moresnet district, Belgium, at various places in Silesia,
Bohemia, Spam and Australia In the United States it occurs in veins at
Lubec, Me , at Rossie, St Lawrence Co , N Y , at PhoenL\ville, Penn , at
Austin's Mines in Wythe Co , Va , and at many other places It is
mined for silver in Mexico, at Leadville, Colo , at various points in
Montana, in the Cceur d'Alene region in Idaho and at many other places
in the Rocky Mountain region
The most extensive galena deposits in this country are in Missouri,
m the corner made by the states of Wisconsin, Illinois and Iowa, and
in Cherokee Co , Kansas In these districts the galena, associated
with sphalerite (ZnS), pynte (FeS2), smithsomte (ZnCOs), calamine
((ZnOH)2SiO3), cerussite (PbC03), calcite (CaCOa) and other minerals,
fills cavities in limestone
Extraction of Lead and Silver from Galena — The ore is first crushed
and concentrated by mechanical or electrostatic methods, and the
concentrates are roasted to convert them into oxides and sulphates
The mass is then heated without access of air, sulphur dioxide being
driven off, leaving metallic lead carrying impurities, or a mixture of
lead and silver
The processes employed in refining the impure lead vary with the
nature of the impurities
Uses — Galena is employed to some extent in glazing common
stoneware It is also used in the preparation of white lead and other
pigments As has alrercly been stated, it is the most important ore of
lead and a very important ore of silver
The metal lead finds many uses in the arts Its most common
use is for piping Its alloys, type metal, pewter and babbitt metal
have already been referred to (p 74) Solder is an alloy of tin and lead,
Wood's metal a mixture of lead, bismuth, tin and cadmium The spe-
cial characteristic of Wood's alloy is its low fusion point (70°)
Production —The total production of galena by the different coun-
tries of the world cannot be given, but the world's production of lead
in 1912 was 1,277,002 short tons The total quantity of lead pro-
duced by the United States from domestic ores in the same year was
about 415,395 tons, valued at $37,385>55° M°st of this was obtained
84 DESCRIPTIVE MINERALOGY
from galena About 171,037 tons were soft lead, smelted from ores
mined mainly for their lead and zinc contents, and the balance from
ores mined partly for their silver The importance of galena as an ore
of silver may be appreciated from the fact that of the $39,197,000
worth of this metal produced in the United States during 1912, silver
to the value of about $12,000,000 was obtained from lead ores or from
mixtures of lead and zinc ores
Altaite (PbTe) and clausthalite (PbSe) both resemble galena m
appearance Both occur commonly in fine-grained masses, but they
are also found in cubic crystals Altaite is tin-white, tarnishing to
yellow or bronze, and clausthahte is lead-gray Their hardness is 2 5-3
and specific gravity about 8 i They are associated with silver and lead
compounds principally in the silver mines of Europe and South America
Altaite is known also from several mines in California, Colorado and
North Carolina They are distinguished from one another and from
galena by the tests for Te and Se
CHALCOCITE GROUP
The chalcocite group includes four or five cuprous and argentous
sulphides, selemdes and tellundes They all crystallize in the ortho-
rhombic system (rhombic bipyramidal class) often with an hexagonal
habit, and are isomorphous The best known members of the group
are chalcoc^te (Cu2S) and stromeyente (Cu AgJgS, but only the first-
named is common Although these minerals are orthorhombic, never-
theless Cu2S is known to exist also in isometric crystals, in which form
it is isomorphous with argentite Moreover, stromeyente is an iso-
morphous mixture of Ag2$ and Cu2S Therefore, it is inferred that
and AggS are isomorphous dimorphs
Chalcocite (Cu2S)
Chalcocite (Cu2S), the cuprous sulphide, is an important ore of
copper though by no means as widely spread as the iron-copper sul-
phide, chalcopyrite It is usually found in black masses with a dull
metallic luster and as a black powder, though frequently also in crys-
tals It is a common constituent of the enrichment zone of many veins
of copper ores,
The best analyses of chalcocite agree closely with the formula
given above, requiring the presence of 20 2 per cent of sulphur and
79 8 per cent of copper Iron and silver are often present in the mineral
in small quantity
SULPHIDES, TELLURIDES, ETC 85
In crystallization chalcocite is orthorhombic (rhombic bipyramidal
class) with the axial ratio 5822 . i 9701 Its crystals contain as
their predominant forms oP(ooi), ooP(no), ooP 00(010), P(in),
a series of prisms of the general symbol -P(iiA). and several bra-
m
chydomes Many cf the crystals are elongated parallel to #, and
others are so developed as to possess an hexagonal habit (Fig 31)
Twins are common according to several laws When the twinning plane is
|P (112) the twins are usually cruciform (Fig 32) The zone ooi— oio
is often striated through oscillatory combinations iioAiib=6o° 25'
The cleavage of chalcocite is indistinct, its fracture is conchoidal
Its hardness is 2 5-3 and density about 5 7. Its streak, like its color,
FIG 31 FIG 32
FIG 31 — Chalcocite Crystal oP, ooi (c), « p So , oio (ft), °o P, no (m), 2? £ ,
021 (d), |P w, 023 (<0, P, iii (p) and JP, 113 00
FIG 32 — Complex Chalcocite Twin, with °o P, no (m) and |P, 112 (p) the Twinning
Planes
is nearly black, but exposed surfaces are often tarnished blue or green,
probably through the production of thin films of other sulphides like
covellite (CuS), chalcopynte (FeCuSa), etc The mineral is an excel-
lent conductor of electricity
In the open tube or on charcoal chalcocite melts and yields sul-
phurous fumes
When mixed with Na2COs and heated a copper globule is produced.
The mineral dissolves in nitric acid with the production of a solution
that yields the test for copper.
Upon exposure to the air chalcocite changes readily to the oxide,
cupnte (CusO), and the carbonates, malachite and azurite. In the
presence of siliaous solutions it may give rise to the silicate, chrysocolla
(P 44i) .
A pseudomorph of chalcocite after galena is known as Aomnfe.
86 DESCRIPTIVE MINERALOGY
It occurs at the Canton Mine m Georgia and in the Polk Co copper
mines in Tennessee Pseudomorphs after many other copper min-
erals are common
Chalcocite is recognized by its color and crystallization Massive
varieties are distinguished from argentite by greater bnttleness and the
reaction for copper, from bormte (CusFeSs) by the fact that it is not
magnetic after roasting
Syntheses — Crystals of chalcocite have been made in many ways,
more particularly by heating the vapors of CuCb and H^S, and by
gently warming CuaO in B^S Measurable crystals have been observed
on old bronze that has been immersed m the waters of hot springs for
a long time
Occurrence , Localities and Origin —The mineral is a common prod-
uct of the alteration of other copper compounds in the zone of secondary
enrichment of sulphide veins. It is therefore present at most localities
of copper minerals One of the best known occurrences is Butte,
Mont
Fine crystals of chalcocite occur in veins and beds at Redruth and
at other places m Cornwall, England, at Bristol m Connecticut, and
at Joachunthal in Bohemia The massive variety is known at many
places In the United States it occurs m red sandstone at Cheshire
in Connecticut It is found also in large quantities near Butte City in
Montana, and in Washoe and other counties in Nevada, and indeed
in the veins of most copper producing mines In Canada it is present
with chalcopynte and bormte at Acton, Quebec, and at several places
in Ontario north of Lake Superior
Extraction of Copper — Chalcocite rarely occurs alone in large
quantity. In ores it is usually mixed with other compounds of copper,
and is treated with them in extracting the metal (see p. 133).
Stromeyerite ((Ag Cu)2S) is usually massive, but it occurs also in
simple and twinned crystals similar to those of chalcocite Their axial
ratio is 5822 i : 9668, almost identical with that of chalcocite The
mineral is opaque and metallic Its color and streak are dark steel-
gray Its hardness is 2 5-3 and density about 62 It is soluble m
nitric acid It occurs associated with other sulphides in the ores of
silver and copper mines at Schlangenberg, Altai, Kupferberg, Silesia,
Coquimbo, Copiap6, and other places in Chile, and in a few mines m
California, Arizona, and Colorado,
SULPHIDES, TELLURIDES, ETC 87
BLENDE GROUP
The blende group of minerals comprises a series of compounds whose
general formula like that of the galena group is RQ In the blendes R
stands for Zn, Cd, Mn, Ni and Fe and Q for S, Se and Te
The blendes are ail transparent or translucent minerals of a lighter
color than galena They constitute an isodimorphous group of a dozen
or more members crystallizing in the tetrahedral division of the regular
system (hextetrahedral class), and in hemimorphic holohedral forms of
the hexagonal system (dmexagonal-pyramidal class) The group may
be divided into two subgroups known respectively as the sphalerite
and the wurtzite groups
SPHALERITE DIVISION
The most important member of this division of the blende group is
the mineral sphalerite. This, like the other less well known members,
crystallizes in the hemihedral division of the regular system with various
tetrahedrons as prominent forms The other members of the group
are alabandite (MnS), and an isomorphous mixture of FeS and NiS,
pentlandite
Sphalerite (ZnS)
Sphalerite, one of the very important zinc ores and one of the most
interesting minerals from a crystallographic standpoint, occurs in amor-
phous and crystalline masses and in handsome crystals and crystal groups
Botryoidal and other imitative masses are common
Pure white sphalerite consists of 67 per cent of Zn and 23 per cent of
sulphur The colored varieties usually contain traces of silver, iron,
cadmium, manganese and other metals Sometimes the proportion of
the impurities is so large that the mineral containing them is regarded as
a distinct variety Two analyses of American sphalerites are as follows
S Zn Cd Fe Total
Franklin Furnace, N J 32 22 67 46 tr 99 68
Jophn, Mo 32 93 66 69 42 100 04
The hemihedral condition of sphalerite is shown in the predominance
of tetrahedrons among its crystal forms and by the symmetry of its
-Q3. _
etched figures (Fig. 33). Its most common forms are — ~(321) and
other hextetrahedrons, ±—(221), ^-(331) and other deltoid-dodeca-
88
DESCRIPTIVE MINERALOGY
hedrons and ±303(311) and other tristetrahedrons In addition,
ooO<»(ioo) and ooO(no) are quite common (Fig 34) Twins are
abundant Their twinning plane is 0 and their composition face either
0 (Fig 35), or a plane perpendicular to this Through twinning, the
crystals often assume a rhombohedral habit
The cleavage of sphalerite is perfect pardlel to ooO(no) From a
compact mass of the mineral a fairly good dodecahedron may some-
times be split Its fracture is conchoidal When pure the mineral is
transparent and colorless As usually found, however, it is yellow,
translucent and black, brown, or some shade of red Its streak is
brownish, yellow or white. The yellow masses look very much like
FIG 33
FIG 34
FIG 35
FIG 33 — Tetrahedral Crystal of Sphalerite Bounded by oo 0 °o (101) and ±O (in
and ill), Illustrating the Fact that Its Octahedral Faces Fall into Two Groups
FIG 34 —Sphalerite Crystal oo 0, no (<*), and-f —-, 311 (m)
FIG 35 — Sphalente Octahedron Twinned about 0(ni)
lumps of rosin. The hardness of sphalerite is between 3 5 and 4, and its
density about 4 Its luster is resinous The minei al is difficultly fusible,
and is a nonconductor of electricity Its index of refraction (ri) for
yellow light is 2 369.
Sphalerite when powdered always yields tests for sulphur under
proper treatment On charcoal it volatilizes slowly, coating the coal
with a yellow sublimate when hot, turning white on cooling When
moistened with a dilute solution of cobalt nitrate and heated m the
reducing flame, the white coating of ZnO turns green The mineral dis-
solves in hydrochloric acid, yielding sulphuretted hydrogen
By oxidation sphalerite changes into the sulphate of zinc, and by
other processes into the silicate of zinc, calamine, or the carbonates,
smithsonite and hydrozincite.
SULPHIDES, TELLURIDES, ETC 89
Syntheses —Sphalerite crystals have been made by the action of
upon zinc chloride \ apor at a high temperature They are also often
produced in the flues of furnaces in which ores containing zinc and sul-
phur are roasted
Occurrence and Origin — Sphalerite occurs disseminated through lime-
stone, in streaks and irregular masses in the same rock, and in veins cut-
ting crystalline and sedimentary rocks It is often associated with
galena The material in the veins is often crystallized Here it is asso-
ciated with chalcopynte (CuFeS2), fluonte (CaF2), bante (BaSCX),
sidente (FeCOs), and silver ores When in veins it is in some cases the
result of ascending hot waters and in other cases the product of down-
ward percolating meteoric water. Much of the disseminated ore is a
metamorphic contact deposit.
Localities — Crystallized sphalerite is found abundantly at Alston
Moor, Cumberland, England, at vanous places in Saxony, in the Bin-
nenthal, Switzerland; at Broken Hill, N S Wales, and in nearly all
localities for galena. Handsome, transparent, deavable masses are
brought from Pilos de Europa, Santander, Spain. Stalactites are
abundant near Galena, 111
The principal deposits of economic importance in America are those
in Iowa, Wisconsin, Missouri and Kansas, where the sphalerite is asso-
ciated with other zinc compounds and with galena forming lodes in
limestone, and at the silver and gold mines of Colorado, Idaho and Mon-
tana
Extraction of the Metal — In order to obtain the metal from sphalerite,
the ore is usually first concentrated by flotation or other mechanical
processes. The concentrates are then converted into the oxide by roast-
ing and the impure oxide is mixed with fine coal and placed in clay retorts
openmg into a condenser. These are gradually heated The oxide is
reduced to the metal, which being volatile distils over into the con-
denser, where it is safely caught. Other processes are based on wet
chemical methods
Uses of Zinc — Zinc is used extensively in galvanizing iron wire and
sheets It is also employed in the manufacture of important alloys
such as brass, and in the manufacture of zmc white, which is the oxide
(ZnO), and other pigments A solution of the chloride is used for pre-
serving timber. Argentiferous zinc is the source of a considerable quan-
tity of silver.
Production — The figures showing the quantity of sphalerite pro-
duced in the zinc-producing countries are not available The total
amount of metallic zmc produced in the year 1912 was 1,070,045 tons,
90 DESCRIPTIVE MINERALOGY
valued at $44,699,166, of which the United States produced from domestic
ores 323,907 tons, and in addition used, in the making of zinc compounds,
about 55,000 tons Of this aggregate, Missouri produced about 149,560
tons Most of the metal was obtained from sphalerite, but a large
part came from other ores The quantity of silver produced in refining
zinc ores was 664,421 oz , valued at $408,619
Alabandite (MnS) is isomorphous with sphalerite It usually
occurs, however, in dense granular aggregates of an iron-gray color
Its streak is dark green It is opaque and brittle Its hardness is 3-4
and density 39 It is not an electrical conductor When heated on
charcoal in the reducing flame it changes to the brown oude of man-
ganese and finally melts to a brown slag It is soluble ui dilute HC1
with the evolution of EkS Alabandite occurs with other sulphides at
Kapnik, Hungary, at Tarma, Peru, at Puebla, Mexico, and m the
United States at Tombstone, Arizona, and on Snake River, Summit Co ,
Colorado
Pentlandite ((Fe Ni)S) may belong to this group Iron is frequently
found in crystallized sphalerite Its sulphide, therefore, may be isomor-
phous with sphalerite, in \\hich case pentlandite, which is probably an
isomorphous mixture of NiS and FeS, would also belong m the sphal-
erite group The mineral occurs in light bronzy yellow, granular masses
with a distinct octahedral cleavage, a hardness of 3 5-5 and a density of
46 It is a nonconductor of electricity Pentlandite occurs with
chalcopynte (CuFeS2) and pyrrhotite (FerSg), at Sudbury, Ontario,
where it is probably the constituent that furnishes most of the nickel
(seep 92)
It is distinguished from pyrrhotite, which it resembles in appearance,
by its cleavage and the fact that it is not magnetic Moreover, it
weathers to a brassy yellow color, while pyrrhotite weathers bronze
WURTZITE DIVISION
The wurtzite group comprises only two or three members, wurt.iie
(ZnS), greenoMe (CdS), and possibly pyrrhottte (FenSH+1) All crys-
tallize m the holohedral division of the hexagonal system and the first
two are unquestionably heimmorphic (dihexagonal pyramidal class)
Pyrrhotite is the most common.
Wurtzite (ZnS) is one of the dimorphs of ZnS, sphalerite being the
other. It occurs in brownish black crystals, m masses and m fibers
SULPHIDES, TELLURIDES, ETC 91
Its crystals are combinations of ooP(ioib) with 2^(2021) and
oP(oooi) at one end, and a series of steeper pyramids at the
other Their axial ratio is i : 8175 The a&gk ion Aoili=4o° 9',
2P(022l) A2P(022I) = 52° 2Jf
The mineral is brownish black to brownish yellow and its streak
is brown Its hardness is between 3 and 4 and its sp gr is about 4
It conducts electricity very poorly In chemical and physical prop-
erties it resembles sphalerite Its crystals ha\e been produced by
fusing a mixture of ZnSO.4, fluonte and barium sulphide They are
frequently observed as furnace products
Wurtzite occurs as crystals at the original Butte Mine, Butte,
Montana, and in a mine near Benzberg, Rhenish Prussia, at both
places associated \\ith sphalerite They also occur \uth silver ores near
Oruro and Chocaya, Bolivia, and near Quispisiza, Peru
Greenockite. — Greenockite (CdS) is completely isomorphous with
wurtzite Its crystals have an axial ratio
i ' 8109 In general habit they are like
those of wurtzite but they contain many more
planes (Fig 36) The angle ioTiAoiTi =
39° 58 Crystals are rare and small The
mineral usually occurs as a coating on other
minerals, especially sphalerite Its color is
honey to orange-yellow, its streak orange- FIG 36 —Greenockite Crys-
yellow, and its luster glassy or resinous It tal OOP, ioT<^(w), aP,
is transparent or translucent and is brittle 2°?x ^> ^IOIJL^and
TII j j A i_ ± °F» o001 (c) (The form
Its hardness is 3-3 5 and density about 4 9 ip> Iol2 (l) ls often pres-
Its index of refraction w=2 688 When ent at the upper end of
heated in the closed tube it becomes carmine, the crystals )
but it changes to its original color on cooling.
It yields the usual reactions for sulphur and cadmium, and dissolves
in HC1, yielding H2S
Crystals have been obtained by melting a mixture of CdO, BaS,
and CaF2, and by heating cadmium in an atmosphere of EfeS to near
fusing point The mineral is a common furnace product Greenockite
crystals occur with prenmte at Bishoptown, Scotland, and as coatings
on sphalerite in the zinc regions of Missouri and Arkansas, and at
Fnedensville, Pennsylvania,
92 DESCRIPTIVE MINERALOGY
Pyrrhotite (FenSn+i)
Pyrrhotite, or magnetic pyrite, occupies the anomalous position
of being one of the most important ores of nickel, whereas it is essen-
tially a sulphide of iron The name is really applied to a series of
compounds whose composition ranges between FesSo and Feu>Si7
The crystallized material is in some cases FerSs, and in others, FenSi2
It is probably a solid solution of FeS2 or S in the sulphide of iron (FeS)
As usually found, pyrrhotite is in bronze-gray granular masses, that
tarnish rapidly to bronze on exposure to the air Good crystals of
the mineral are rare.
Analyses of pyrrhotite vary widely The percentages of Fe and S
corresponding to FeySs are Fe, 60 4, S, 39 6, and those corresponding
to FenSi2 are Fe, 61 6, S, 38 4 Much of the mineral contains in addi-
tion to the iron and sulphur sufficient nickel to render it an ore of this
metal, but it is probable that the nickel is present in pentlandite (see
p 90) or some other nickel compound embedded in the pyrrhotite
Analyses of pyrrhotite from various localities are
S Fe Co Ni Total
Schneeberg, Saxony 39 10 6r 77 tr 100 87
Brewster, NY 37 98 61 84 25 100 07
Sudbury, Ontario 38 91 56 39 4 66 99 96
Gap Mine, Penn. 38 59 55 82 5 59 100 oo
The few crystals of pyrrhotite known are distinctly hexagonal in
habit with a c=i i 7402 They are com-
monly tabular or acutely pyramidal, but it
has not been established that they are hemi-
morphic, although the almost universal pres-
ence of FeS in crystals of wurtzite would
FIG 37 -Pyrrhotite Crystal mdlcate that the two substances are isomor-
oP, oooi (c), P, ion (s); , _, ^ , , . f
4P, 4041 («), and COP, Phous The tabular crystals possess a broad
I0lo (m) basal plane, which surmounts hexagonal prisms
ooP(ioTo) and oop2(ii2o); and a series of
pyramids, of which 2P(2O2i), JP(ioT2), P(ioli) and P2(ri22) are the
most frequent (Fig 37 ) The angle loli AoiTi = S3° «;
The cleavage of pyrrhotite is not always equally distinct When
marked it is parallel to ooP2(ii2o) There is also often a parting
parallel to the base Its fracture is uneven The mineral is brittle.
It is opaque, and has a metallic luster Its color varies between bronze-
SULPHIDES, TELLURIDES, ETC 93
yellow and copper-red, and its streak is grayish black Its hardness is
a little less than 4 and its density about 4 5 All specimens are magnetic
but the magnetism varies greatly in intensity, being at a maximum in
the direction of the vertical axis The mineral is a good conductor of
electricity.
Pyrrhotite gives the usual reactions for iron and sulphur, and some-
times, in addition, the reactions for cobalt and nickel It is decom-
posed by hydrochloric acid with the evolution of EbS, which may
easily be detected by its odor.
From the many sulphides more or less closely resembling pyrrhotite
in appearance, this mineral may easily be distinguished by its color
and density and by its magnetism
Syntheses — Crystals may be obtained by heating iron wire or
Fes04, or dry FeCk to redness in an atmosphere of dry HoS and by
heating Fe in a closed tube with a solution cf FcCls saturated with
H2S
Occurrence, Locd^t^es and Origin — Pyrrhotite occurs completely
filling vein fissures, and also as crystals embedded in other minerals
constituting veins It occurs also as impregnations in various rocks
and as a segregation in the coarse-grained basic rock known as nonte,
where it is believed to have separated from the magma producing the
rock It may also in some cases be a product of metamorphism on the
borders of igneous intrusions
It is found at Andreasberg, Harz, Bodenmais, Bavaria, Minas
Geraes, Brazil, various points in Norway and Sweden, and on the
lavas of Vesuvius In North America crystals occur at Standish, Maine,
at Trumbull, Monroe Co , N Y , and at Elizabethtown, Ontario
The mineral has been mined at Ducktown, Tenn , at Ely, Vermont,
and at Gap Mine, Lancaster Co , Penn
Its mines at present, however, are at Sudbury, in Ontario, where the
mineral is associated with magnetite, chalcopynte and pentlandite
((Fe Ni)S) on the lower border of a great mass of igneous rock (norite).
Besides these there are present also embedded in the pyrrhotite
small quantities of other minerals, so that the ore as mined is very
complex.
Pyrrhotite is sometimes found altered to pyrite, to limomte and to
siderite (FeC03)
Extraction — Pyrrhotite is crushed and roasted to drive off the
greater portion of the sulphur It is then placed in a furnace and
smelted with coke and quartz The nickel, copper and some of the
iron, together with some of the fused sulphides, collect as a matte in the
94 DESCRIPTIVE MINERALOGY
bottom of the furnace from which it is withdrawn from time to time
The matte is next roasted to transform the iron it contains into oxides
and the remaining nickel and copper are separated by patented or secret
methods
Uses —The mineral is sometimes worked for the sulphur it con-
tains Its principal use, however, is as a source for nickel, nearly all of
this metal used in America coming from the nickehferous variety found
at Sudbury, Ontario
The metal nickel has come into extensive use in the past few years
in connection with the manufacture of armor plate for warships The
addition of a few per cent of nickel to steel hardens it and increases
its strength and elasticity
Nickel is also extensively used in mckel-platmg and in the manufac-
ture of alloys German silver is an alloy of nickel, copper and zinc The
nickel currency of the United States contains about 25 per cent Ni and
75 per cent Cu Monel metal is a silver-white alloy containing about
75 per cent Ni, i per cent Fe and 29 per cent Cu It is stronger than
ordinary steel, takes a brilliant finish and is impervious to acids It is
made directly at Sudbury, Ont , by smelting
Production —The production of pyrrhotite and chalcopyrite (CuFeS)
at the Sudbury mines in 1912 amounted to 737,584 short tons The
value of the matte produced was $6,303,102, and the value of nickel con-
tained in it was about $16,000,000 About half of the nickel was used
in America, the remainder, amounting to $8,515,000, was exported, after
being refined in the United States Formerly the United States pro-
duced a considerable quantity of nickel from domestic ores, most of
it from pyrrhotite, but the mines have been closed down within the past
few years. It is, however, produced as a by-product in the refining
of copper ores to the amount of about 325 tons annually, This is worth
about $260,000 (see also p, 400).
MILLERITE GROUP
This group comprises sulphides, arsenides and antimonides of nickel.
It includes the minerals millmte (NiS),mccohte (NiAs), ante (Ni(Sb • As))
bwthauptite (NiSb) and a few others Of these only millente and nic-
colite are at all common The minerals all crystallize m the hexagonal
system, possibly in the rhombohedral division (ditrigonal scalenohedral
class). Well defined crystals are, however, rare and often capillary so
that their symmetry has not been determined with certainty.
SULPHIDES, TELLURIDES, ETC 95
Mfflerite (NiS)
Millerite is easily recognized by its brass-yellow color It occurs
most frequently in slender hair-like needles, often aggregated into tufts
or radial groups, or, woven together like wads of hair, forming coatings
on other minerals
Pure millente contains 35 3 per cent sulphur and 64.6 per cent nickel
It frequently contains also a little Co and Fe.
Crystals are thin, acicular or columnar with prismatic and rhom-
bohedral faces predominating, and an axial ratio of i 330, or of i : 9886
if the rhombohedron 311(0331) is taken as the ground form
The mineral is elastic Its hardness is 3-3 5 and density about 5 5.
It is opaque and brassy yellow Its streak is greenish black. It is an
excellent conductor of electricity
The mineral yields sulphurous fumes in the open tube. After roast-
ing it gives, with borax and microcosmic salt, a violet bead when heated
in the oxidizing flame of the blowpipe On charcoal with NaaCOs it
yields a magnetic globule
Synthesis — Bunches of yellow acicular crystals of N1S have been
formed by treatment of a solution of NiSO^ with H^S, under pressure.
Localities — Millerite occurs as long acicular crystals in cavities in
other minerals at Joachimthal, in Bohemia, and at many places in
Saxony In the United States it forms radiating groups in cavities in
hematite (F&Os) at Antwerp, NY At the Gap Mine, Lancaster Co ,
Penn , it forms coatings on other minerals and at St Louis, Mo and
at Milwaukee, Wis , it occurs in delicate tangled tufts in geodes in lime-
stone, Nowhere does it occur in sufficient quantity to constitute an ore.
Niccolite (NiAs)
Niccolite usually occurs massive, though crystals are known It is
of economic importance only in a few localities
Theoretically, the mineral contains 56 10 per cent As and 43 90 per
cent Ni, but as usually found it contains also Sb, S, Fe and often small
quantities of Co, Cu, Pb and Bi
Its crystals, which are rare, are hexagonal and hemimorphic (prob-
ably dihexagonal pyramidal class), with a : c=i : 8194 The prism
ooP(ioTo), and oP(oooi) are the predominant forms, with the
pyramids P(ioTi) and ^(5057) less well developed The angle
The mineral is pale copper-red and opaque It has a brownish
96 DESCRIPTIVE MINERALOGY
black streak. Its hardness is about 5 and its density 7 6 The surfaces
of nearly all specimens are tarnished with a grayish coating The min-
eral is a good conductor of electricity
In the open tube mccohte yields arsenic fumes and often traces of
862 On charcoal with Na2COs it yields a metallic globule of nickel
It dissolves in HNOs with the precipitation of AsgOa The apple-green
solution, thus produced, becomes sapphire-blue on addition of ammonia
Its peculiar light pink color and its reactions for arsenic and nickel
distinguish mccohte from all other minerals, except, perhaps, breit-
kaupttte, which, however, contains antimony
Occurrence — Niccohte occurs principally in veins in crystalline
schists and in metamorphosed sedimentary rocks, associated with silver
and cobalt sulphides and arsenides
Local^foes — The principal locality for mccohte in North America is
Cobalt, Ontario, where it is found with native silver and silver, cobalt,
and other nickel compounds, all of which are thought to have been de-
posited by hot waters emanating from a mass of diabase In Europe it
is abundant at Joachimsthal in Bohemia, and at a number of other
places in small quantity
Although rich in nickel, the mineral is not used as an ore at present,
except to a very minor extent, most of the nickel of commerce being
obtained from other compounds (see p 94)
Breithauptite (NiSb) is rare It is of a light copper-red color, much
brighter than that of mccohte, and its streak is reddish brown Its hard-
ness is 5 5 and density about 7 9 Its crystals are hexagonal tables
with an axial ratio i i 294, and a distinct cleavage parallel to oP(ooi)
It usually occurs m dendritic groups, m foliated and finely granular
aggregates and in dense masses It is a frequent furnace product, when
ores containing Ni and Sb are smelted It is found at Andreasberg, Harz ,
at Sarrabus, m Sardinia, at Cobalt, Ont , and at a few other places It
is distinguished from mccohte by its deeper color and its content of Sb.
Covelhte (CuS)
Covellite, or indigo copper, is the cupric sulphide, chalcocite being
the corresponding cuprous salt It is called indigo copper because of
the deep blue color of its fresh fracture. It is often mixed with other
copper compounds from which it has been derived by alteration It
usually occurs massive, but crystals are known It is an unimportant
ore of copper.
SULPHIDES, TELLURIDES, ETC 97
The theoretical composition of the mineral is 33 56 per cent S,
66 44 per cent Cu It usually, however, contains also a little iron and
often traces of lead and silver
Crystals of covellite are not common. They are hexagonal \\ith
a c-i 3 972 and their habit is usually tabular The forms observed
are oP(oooi), oo P(iolo), P(ioTi) and JP(ioT4) icTi /\oi Ti = 77° 42'.
The mineral has one perfect cleavage parallel to oP(oooi) In
thin splinters it is flexible Its hardness is i 5-2 and density about
4 6 Its color is dark blue and its streak lead-gray to black It is
opaque, with a luster that is sometimes nearly metallic, but more
frequently dull It is a good electrical conductor
The blowpipe reactions of covellite are like those of chalcocite, with
these exceptions Covellite burns ^ith a blue flame when heated on
charcoal, and yields a sublimate of sulphur in the closed tube
Covellite is distinguished from other minerals than chalcocite by
its reactions for Cu and S and the absence of reactions for Fe. It is
distinguished from chalcocite by its color and density and by the fact
that it ignites on charcoal
Syntheses — The treatment of green copper carbonate with water
and EkS in a closed tube at 8o°-9o° yields small grains of covellite
The mineral has also been produced by the action of HsS upon vapor
of CuCl2, and by treating sphalerite with a solution of copper sulphate
in a sealed glass tube containing C02 at a temperature of iso°-i6o°
for two days
Localities and Origin— The mineral is comparatively rare It is
abundant in Chile and Bolivia and at Butte, Mont , and is found in
crystals on the lava of Vesuvius and elsewhere It usually occurs as
an alteration product of other copper-sulphur compounds, especially in
the zone of secondary enrichment of copper veins
Uses — It is mined with other compounds and used as a source
of copper,
CINNABAR GROUP
This group comprises sulphides, selenides and tellundes of mercury
The group is dimorphous, with its members crystallizing in henuhedrons
of the isometric system (hextetrahedral class) and in tetartohedrons
of the hexagonal system (trigonal trapezohedral class) The isometric
HgS is known as metacmnabante and the hexagonal form as cinnabar
Only the latter is important In addition to these are known the rare
compounds onofnte (Hg(S Se)), tiemanmte (HgSe) and coloradcnte
(HgTe), all of which are isometric
98
DESCRIPTIVE MINERALOGY
Cinnabar (HgS)
Cinnabar is the only compound of mercury that occurs in sufficient
quantity to constitute an important ore Nearly all of the mercury,
or quicksilver, in the world is obtained from it The mineral occurs
both crystallized and massive The ore is a red crystalline mass that
is easily distinguished from all other red minerals by its peculiar shade of
color and its great weight.
Theoretically, it contains 13 8 per cent S and 86 2 per cent Hg
Massive cinnabar is, however, usually impure through the admixture
of clay, iron oxides or bituminous substances Occasionally the quan-
tity of organic material present is so large that the mixture is inflam-
mable.
Though cinnabar is usually granular, massive or earthy, it some-
times occurs beautifully crystallized
in small complex and highly modi-
fied hexagonal crystals that exhibit
tetartohedral forms (trigonal trape-
zohedral class) Usually the crys-
tals are rhombohedral or prismatic
m habit Their axial ratio is
i . i 1453 Planes belonging to
more than 100 distinct forms have
been observed, but the crystals on
which they occur aie usually so
small that few of them are of im-
portance as distinguishing charac-
teristics. The prismatic crystals, which are the most common in
this country, are often bounded by ooR, (rolo) and £R, (4045)
(Fig 38) Others, however, are very complicated Their cleavage is
perfect parallel to oo R(ioTo).
The mineral is slightly sectile It is transparent, translucent or
opaque, is of a cochineal-red color, often inclining to brown, and its
streak is scarlet Its hardness is only 2-2 5 and its density about
8 i It is circularly polarizing and is a nonconductor of electricity
Its dimorph, metacinnabante, on the other hand, is a good conductor
The indices of refraction of cinnabar are co= 2 854, €==3 201
When heated gently in the open tube cinnabar yields sulphurous
fumes and globules of mercury. On charcoal before the blowpipe it
volatilizes completely.
There are only a few minerals with which cinnabar is likely to be
FIG 38 -Cinnabar Crystals with « R,
iolo (m), fR, 4045 (0, £R, 2025
(/), R, loTi (0 and o&, oooi (c)
SULPHIDES, TELLURIDES ETC 99
confused, since its color and streak are so characteristic From all
red minerals but realgar it may easily be distinguished by its sulphur
reaction From realgar it is distinguished by its great density and its
greater hardness
Pseudomorphs of cinnabar after stibnite, dolomite ((Ca Mg)COsJ,
pynte and tetrahednte (a complicated sulpho-salt) have been described
Synthesis — Crystals ha\ e been made b> heating mercury in an aque-
ous solution of HbS
Occurrence Localities and On gin — Cinnabar is usually found in
veins cutting serpentine, limestones, slates, shales and \anous schists
It is associated \Mth gold, various sulphides, especially pynte and mar-
casite (FeS2) calcite (CaCOs), barite (BaSO-i), fluonte (CaF2) and
quartz It is also found impregnating sandstones and other sedimen-
tary rocks, and sometimes as a deposit from hot springs Its deposi-
tion is thought to be the result of precipitation from ascending hot
Crystallized cinnabar occurs at a number of places in Bohemia,
Hungary, Serbia, Austria, Spam, California, Texas, Nevada, and at
ether localities m Europe Asia and South America
The principal deposits of economic importance are at Almaden
in Spain, at Idria in the Province of Carmola, Austria, at Bakhmut
in southern Russia, at various points along the Coast Ranges in Cal-
ifornia, in Esmeralda, Humboldt, Nye and Washoe Counties in Nevada,
at many points in Oregon and Utah, and at Terhngua in Texas The
mineral is also abundant in Peru and in China but in these countries
it has not yet been mined profitably The California cinnabar district
extends for many miles along the Coast Ranges, but at only about a
dozen places is the mineral mined
The Spanish mines, near the city of Cordova, have been worked
for many hundreds of years Much of the ore is an impregnation of
sandstone and quartzite — the mineral sometimes comprising as much
as 20 per cent of the rock mined
Extraction — The metallurgy of cinnabar is exceedingly simple It
consists simply in roasting the ore alone, or mixed with limestone, and
conducting the fumes into a condensing chamber that is kept cool.
The sulphur gases are allowed to escape through the chamber in which
the mercury is collected
Uses of Metal — Mercury finds many uses in the arts Its most im-
portant one is in the extraction of gold and silver by the amalgamation
process It is the essential constituent of the pigment vermilion, which
is a manufactured HgS. In its metallic state it is largely employed in
100 DESCRIPTIVE MINERALOGY
the making of mirrors, of barometers, thermometers and other physical
instruments Some of the salts are important medicinal preparations
while others are used in the manufacture of percussion caps
Production —The world's annual production of quicksilver, all of
which is obtained from cinnabar, is not far from 4,000 metric tons The
United States produced 940 tons in 1912, valued at $1,053,941 Of this
total California yielded 20,524 flasks of 75 Ibs each, valued at about
$863,034, and Texas and Nevada 4,540 flasks valued at $190,907 To
produce these quantities of metal California mined I39>347 tons of ore
and Texas and Nevada 16,346 tons The California ore yielded n Ibs
of metal per ton and the Nevada and Texas ore 20,8 Ibs,
Metacmnabarite (HgS) is generally found as a gray-black massive
mineral with a black streak It is brittle, has a hardness of 3 and a
density of 7 8 It is associated with cinnabar at some of the mines in
California and Mexico, and at a few places in other countries It is
exceedingly rare.
THE METALLIC DISULPHIDES, DISELENIDES AND DIARSENIDES
The disulphides, diselemdes, ditellundes, diarsemdes and dianti-
monides differ from the corresponding monocompounds m that they
contain double the quantity of S, Se, Te and Sb They are divisible
into two groups, one of which comprises sulphides, arsenides and anti-
monides of iron, manganese, cobalt, nickel and platinum, and the other
the tellundes and selemdes of gold and silver,
GLANZ GROUP
The glanz group is an excellent illustration of an isodimorphous group.
Its members are characterized by their hardness, opaqueness, light color
and brilliant luster. Hence the name of the group In composition
the minerals belonging to the group are sulphides, arsenides or anti-
momdes of the iron-platinum group of metals, with the general formula
RQ2 in which R is Mn, Fe, Ni, Co, Pt, and Q=S, As and Sb The com-
position of the more simple members may be represented by the formula
/S
Fe/ | , and of those in which arsenic or antimony replaces a part of the
<As=As\
>Fe.
S y
It is probable, however, that some of the cobalt and nickel arsenides
SULPHIDES, TELLURIDES, ETC 101
are mixtures and that their indicated compositions are only approximate
All members of the group are believed to be dimorphous, crystallizing
in the isometric (dyakisdodecahedral class), and in the orthorhombic
systems (orthorhombic bipyramidal class), though not all have as yet
been found in both forms The most important members of the group, as
at present constituted, are as follows
Isometric Orthorhombic
Pynte FeSg Marcasite
Hauente MnS2
FeAsS Arsenopyrite
FeAs2 Lolhngite
CobalMe CoAsS Glaucodot
Gersdor/tte (Ni Fe)AsS
Korymte (Ni Fe)(As Sb S)2 Wolfachite
Ullmamte NiSbS
Smdtite CoAs2 Safflonte
Ckloanthite NiAs2 Rammdsbergite
Sperryhte PtAs2
The group is divided into two subgroups, the regularly crystallizing
minerals forming the pynte group and the orthorhombic ones the mar-
casite group The most important members of the former group are
pynte, cobaltite, smaltite and chloanthite The most important members
of the marcasite group are marcastte, arsenopynte and lolhngite.
PYRITE
The crystallization of the pyrite group is in the parallel heimhedral
division (dyakisdodecahedral class) of the isometric system. The
occurrence of the form - , 210, is so frequently seen on the mineral
pyrite that it has received the name pyritoid
The group is so perfectly isomorphous that a description of the forms
on one member is practically a description of the forms on all.
Pynte (FcS2)
Pyrite, one of the most common of all minerals, is found under a
great variety of conditions as crystals, as crystalline aggregates and
as crystalline masses It occurs under practically all conditions and in
all situations It is easily recognized by its bright yellow color, its
brilliant luster and its hardness,
102
DESCRIPTIVE MINERALOGY
Pyrite containing, theoretically, 46 6 per cent of iron and 53 4 per
cent of sulphur is usually contaminated with small quantities of nickel,
FTC 39 — Group of Pyrite Crystals in which the Cube Predominate The c
/20oo\
are striated parallel to the edge between oo 0 oo (100) and I — — ) , (210)
cobalt, thallium and other elements An auriferous variety is worked
for gold, yielding in the aggregate a large quantity of the precious
FIG 40 I«K, 4i
FIG 40 — Pynte Crystals on which 0 (in) Predon mates o=0, n i and c
210
FIG 41 — Pynte Crystal with oo 02, 210 (e) and 0, in (a)
metal Sometimes arsenic is present in small quantity Analysis of
the crystals from French Creek, Penn , gave
8=5408, As=o 20, Fe=44 24, Co=i 75, Ni=o 18, Cu=oos, =100 50.
SULPHIDES, TELLURIDE3, ETC
103
The number of forms that have been observed on pynte crystals is
very large Hintze records 86 The cube and the pyntoid ^-^ I
L 2 J
FIG 42 — Group of Pynte Crystals in \\hich ooQ2 (210) Predominates
Daly- Judge Mine, near Park City, Utah (After J W Bmtfaett )
From
(210) are the most common of these, though the octahedron and the
dodecahedron are not rare Four distinct types of crystals may be
recognized, viz those with the cubic (Fig 39),
the octahedral (Fig. 40), and the pyntoid
habits (Figs 41 and 42), and those that are
interpenetrating twins (Fig 43) The cubic
and the pyritoid planes are often striated
parallel to the edges between these faces The
interpenetrating twins are twinned about the
plane 0(ni)
The cleavage of pynte is imperfect and
its fracture conchoidal. The mineral is
brittle Its hardness is 6-6 5 and density
about 5. Its luster is very brilliant and
metallic Its color is brassy yellow and its
streak greenish or brownish black With steel it strikes fire, hence its
name from the Greek word meaning fire. It is a good conductor of
electricity and is strongly thermo-electric.
FIG 43 — Pynte Interpene-
trationTwin Two Pyn-
toids ( «s Os, 210) Twinned
about O in
In the closed tube pynte yields a sublimate of sulphur and a residue
that is magnetic On charcoal sulphur is freed This burns with the
blue flame characteristic of the substance The globule remaining after
heating for some time is magnetic Treated with nitric acid the
mineral dissolves leaving a flocculent residue of sulphur, which when
dried and heated may readily be ignited
Pynte in some of its forms so closely resembles gold that it is often
known as fool's gold There is, of course, no difficulty in distinguishing
between the two metals, since pyrite contains sulphur and is soluble in
nitric acid, while gold contains no sulphur and is insoluble in all simple
acids.
The mineral is most easily confounded with chako pynte (CuFeS>),
though the difference in hardness of the two easily serves to distinguish
them Chalcopynte may be readily scratched with a knife blade or a
file, while pyrite resists both The latter mineral, moreover, contains
no copper
Syntheses — Small crystals of pyrite are produced by the action
of HaS on the oxides or the carbonate of iron enclosed in a sealed tube
heated to 8o°-9o°, also by the passage of EbS and FeCla vapors through
a red-hot porcelain tube.
Occurrence and Origin— Pynte occurs in veins and as grains or
crystals embedded in all kinds of rocks. In rocks it usually appears as
crystals, but in vein-masses it may appear either as crystals, with other
minerals, or as radiating or structureless masses occupying entirely the
vein fissures In slates it often occurs in spheroidal nodules and
concretions of various forms, and also as embedded crystals. The
mineral is the product of igneous, metamorphic and aqueous agencies
Pyrite weathers readily to hmonite. In ore bodies near the
surface it is oxidized. A portion of the mineral changes to FeSQt
which percolates downward and aids in the concentration of any
valuable metals that may be present m small quantity in the ore.
Another portion of the iron remains near the surface in the form of
lunonite This covering of oxidized material is known as the " gossan "
and it is characteristic of all pyrite deposits
Localities — Pynte crystals are so widely distributed that but very
few of its most important occurrences may be mentioned here In the
mines of Cornwall, Eng , and in those on the Island of Elba very large
crystals are found Fine crystals also come from many different places
in Bohemia, Hungary, Saxony, Peru, Norway, and Sweden
In the United States the finest crystals are at Schoharie and Rossie,
N Y ; at the French Creek mines in Chester Co , and at Cornwall,
SULPHIDES, TELLURIDE3, ETC 105
Lebanon Co , Penn , and near Greensboro and Guilford Co , X Carolina
Massive pyrite occurs in great deposits at the Rio Tmto mines in
Spain, at Rowe, Mass , in St Lawrence and Ulster counties, X Y ,
in Louise Co , Va , and in Pauldmg Co , Ga Much of the massive
pynte in the veins of Colorado, California and of the southern states,
from Virginia to Alabama, is auriferous and much of it is mined for the
gold it contains
Uses — Pynte is used principally in the manufacture of sulphuric
acid The mineral is burned in furnaces and the 862 gases thus result-
ing are carried to condensers \\here they are oxidized by fineh divided
platinum or by the oxides of nitrogen The residue, which consists
largely of Fe20s, is sometimes smelted for iron or made into paint
This residue also contains the gold and other \aluable metals that may
have been in the original pyrite.
The sulphuric acid obtained from pyrite enters into many manu-
facturing processes The greater portion of it is consumed in the
artificial fertilizer industry
Production — Pyrite is mined in the United States in Franklin Co ,
Mass , in Alameda and Shasta Counties, California, in Louisa, Pulaski
and Prince William Counties, Va , in Carroll Co , Ga 3 in St Lawrence
Co , N Y , m Clay Co , Alabama, and at the coal mines in Ohio.
Illinois and Indiana where it is a by-product The total production
of the United States in 1912, amounting to 330,928 long tons, was
\alued at $1,334,259 Virginia is by far the largest producer In
addition to this quantity the trade consumed 970,785 tons of imported
ore, most of which came from Spain, and utilized the equivalent of
260,000 tons of pynte m the shape of low grade sulphide copper ores
from Ducktown, Tenn , and zinc sulphide concentrates from the Mis-
sissippi Valley and elsewhere for the manufacture of sulphuric acid.
The total amount of sulphuric acid manufactured in the United States
during 1912 was 2,340,000 short tons, valued at $18,338,019 The total
world production of pyrite is about 2,000,000 tons annually
Small quantities of the mineral are also mined for local consumption
in Lumpkin Co , Georgia, and near Hot Springs, Arkansas Much
aunferous pynte has also been mined in the southern states and the
Rocky Mountain region for the gold it contains This metal is sepa-
rated from the pyrite partly by crushing and amalgamation and partly
by smelting or by leaching processes. In the former case the gold
occurs as inclusions of the metal in the pynte.
106 DESCRIPTIVE MINERALOGY
Cobaltite (CoAsS)
Cobaltite is a alver-nvhite or steel-gray mineral occurring in massive
forms or in distinct crystals exhibiting beautifully their hemihedral
character It is completely isomorphous with the corresponding nickel
compound, gersdorffite (NiAsS), and consequently mixtures of the
two are common
Cobaltite usually contains some iron and often a little nickel
Theoretically, it consists of 19 3 per cent S, 45 2 per cent As and 35 5
Co The compositions of a massive variety from Siegcn, Westphalia,
and that of crystals from Nordmark, Norway, are as follows
As S Co Fe Ni Total
Siegen 45 31 19 35 33 71 i 63 100 oo
Nordmark 44 77 20 23 29 17 4 72 i 68 100 57
The crystallization of cobaltite is perfectly isomorphous with that
of pyrite, though the number of its forms observed is far smaller The
most common planes are those of oo 0 oo (100) , 0(i 1 1 ) and (210)
The cleavage of cobalt is fairly good parallel to oo 0 oo (100) Its
fracture is uneven, its hardness is 5 5 and its density about 6 2 The color
of the mineral, as stated above, varies between silver-white and steel-
gray Its streak is grayish black It is a good conductor of electricity
In the open tube cobaltite reacts for S and As On charcoal it
yields a magnetic globule which when fused with borax on platinum
wire yields a deep blue bead It weathers fairly readily to the rose-
colored cobalt arsenate known as erythnte (Coa(As04)2 SEfeO)
By its crystallization and color cobaltite is distinguished from
nearly all other minerals but those of the same group From most of
these it is easily distinguished by its blowpipe reactions foi sulphur,
arsenic and cobalt
Occurrence and Origin — Cobaltite occurs mainly m veins that are
believed to have been filled by upward moving solutions emanating
from igneous rocks It is associated with compounds of nickel and other
cobalt compounds and with silver and copper ores
Localities — Cobaltite is not very widely distributed Large, hand-
some crystals occur at Tunaberg in Sweden, at Nordmark, Norway,
at Siegen, Westphalia, and near St Just in Cornwall, England It is
found also in large quantity at Cobalt, Ontario, associated with silver
ores and nickel compounds
SULPHIDES, TELLURIDES ETC 107
Uses — Cobaltite is said to be used b\ jewelers in India in the pro-
duction of a blue enamel on gold ornaments It is employed also in the
manufacture of blue and green pigments and in the manufacture of com-
pounds used in small quantity in the various arts Smalt is the most
valuable of the cobalt pigments and is at present the chief commercial
compound of this metal It is a deep blue glass that cheers from
ordinary glass in containing cobalt in place of calcium Smalt is made
from cobaltite and from other cobalt ores b\ fusion \\ith a mixture of
quartz and potassium carbonate Certain cobalt compounds are sug-
gested as excellent driers for oils and varnishes The mineral is also
utilized as an ore of cobalt, \\hich in the form of stelhte, an alloy com-
posed of 70 per cent cobalt, 15 per cent chromium and 15 per cent
molybdenum or tungsten, bids fair to acquire a large use as a material
for the manufacture of table cutlery and edged tools The use of the
metal has also been suggested as a material for coinage in place of
nickel.
Production — Most of the cobalt of commerce is handled by the
trade in the form of the oxide It is produced from the \ anous cobalt
minerals, mainly as a by-product in the extraction of nickel, and hence
ver> little is obtained from ccbaltite The mines at Cobalt, however,
have furnished a large quantity of cobaltite and smaltite \uthin the past
few years and these have gone into the manufacture of the oxide, of
uhich about 515 tons -\\ere produced in 1912, ha\mg a \alue of
$317,165
Smaltite (CoAs>)
Smaltite is another important ore of cobalt It is found in crystals
and masses
Its theoretical composition is 71 88 per cent As and 28 12 per cent
Co, though it usually contains also S, Ni, Fe and frequently traces of
Bi, Cu and Pb Since it is isomorphous \uth the arsenide of nickel
chloanthite (NiAs2), mixed crystals of the t\\o are common Moreover,
sharply defined crystals have been found to consist of mechanical mix-
tures of several compounds
Smaltite occurs in small crystals of cubical habit with ooOoo (100),
0(in) and various pyritoids predominating
The mineral is tin-white to steel-gray, and opaque, and has a grayish
black streak It is often covered ^ith an iridescent or a gray tarnish.
Its cleavage is indistinct, its fracture uneven, its hardness 5-6 and
density 6 3-7 It is a good electrical conductor
Before tie blowpipe on charcoal smaltite yields arsenic fumes and a
108 DESCRIPTIVE MINERALOGY
magnetic globule of metallic cobalt It is soluble in HNOs, yielding a
rose-colored solution and a precipitate of As2Os
The mineral is fairly easily distinguished from most other minerals
by its color and blowpipe reactions From cobaltite it is distinguished by
the lack of S From a few others that are not described in this volume
it can be distinguished by its crystallization or by quantitatn e analysis
Synthesis — Smaltite crystals are produced when hydrogen acts at a
high temperature upon a mature of the chlorides of cobalt and arsenic
Occurrence and Ongm —Smaltite is found associated with cobaltite
in nearly all of its occurrences It is especially abundant at Cobalt, Out
As in the case of most other cobalt minerals, its presence is indicated by
deposits of rose-colored erythnte which coat its surfaces wherever these
are exposed to moist air Its methods of occurrence, origin and uses
are the same as for cobaltite (p 107).
Chloantfaite (NiAso) resembles smaltite in most of its characteris-
tics The two minerals grade into each other through isomorphous
mixtures Those mixtures in which the cobalt arsenide is in excess
are known as smaltite, while those in which NiAs predominates arc
called chloanthite The pure chloanthite molecule is Ni= 28 i per cent,
As =7 1 9 per cent
The two minerals can be distinguished when unmixed with one
another by the blowpipe reactions for Co and Ni In mixed ciysUis
the predominance of one or the other arsenides can be determined only
by quantitative analysis
Chloanthite containing much iron is distinguished as thathamite,
from Chatham, Conn , where it occurs with arsenopynte and niccohte in
a mica-slate
The mode of occurrence of chloanthite and the localities at which
it is found are the same as in the case of smaltite.
Spenyhte (PtAs2)
Sperryhte is extremely rare It is referred to here because it is the
only platinum compound occurring as a mineral Chemically, it is
43 S3 Per cent As and 56 47 per cent Pt, but it contains also small quan-
tities of Sb, Pd and Fe
Its crystals are simple They contain only 0(iu), ooOoo(ioo),
oo 0(no) and several pyntoids Their habit is usually octahedral or
cubical
The mineral is opaque and tin-white, and its streak black Its hard-
ness is 6-7 and density 10 6
SULPHIDES, TELLURIDE3, ETC 109
In the closed glass tube it remains unchanged, but in the open tube
it gives a sublimate of As^Os When dropped upon red-hot platinum
foil it immediately melts, giving rise to fumes of As20s, and forming
blisters on the foil that are not distinguishable from the original platinum
in color or general character It is shnvh soluble in concentrated HC1
and aqua regia
Synthesis — The mineral has been produced by leading arsenic fumes
over red-hot platinum in an atmosphere of h\drogen
Occurrence and Localities — Sperrylite occurs as little crystals com-
pletely embedded in the chalcopynte (CuFeSo) and the gossan of a
nickel mine, and in the chalcop\nte of a gold-quartz vein near Sudbury,
Ontario, in covelhte at the Rambler Mine, Encampment, \V\ormng,
and as flakes in the sands of streams in the Co\\ee Valle\ , Macon Co , Ga
The flakes resemble very close,!} native platinum, from which they are
of course, easily distinguished by the test for arsenic
Uses — The sperryhte from Sudbury and \V} ommg furnish much of
the platinum produced in the United States (see p 64)
MARCASITE Dl\ ISIOX
Three members of the marcasite group are important, all are inter-
esting from the fact that they are so alike in their cr\stalhzation that a
description of the forms belonging to any one of them might serve as a
description of those belonging to all others The crystallization of the
group is orthorhombic (rhombic bipyramidal class), with an axial ratio
approximately a b ' c= 7 1:12
Marcasite (FeS2)
Marcasite, the dimorph of pynte, resembles this mineral so closely
that in massive specimens it is difficult to distinguish between the two
They are nearly alike in hardness, in color and in chemical properties
Marcasite is a little lighter m color than pynte Its density is less
(about 4 9), and it possesses a greater tendency to tarnish on exposed
surfaces
This tarnish indicates that the mineral is more susceptible to altera-
tion than is pynte One of the products of this alteration is ferrous sul-
phate, which may often be detected by its taste upon touching the tongue
to specimens of the mineral In crystallized specimens there is not the
least difficulty in distinguishing between them, suice their crystallization
is very different
Marcasite is orthorhombic (rhombic bipyramidal class), with the
110
DESCRIPTIVE MINERALOGY
axial ratio 7662 i i 2342 Its simple crystals often possess a tabular
or a pyramidal habit (Figs 44 and 45) In the former case oP(ooi) is
the predominant face, and m the latter case the two domes P 60 (101)
FIG 44 FIG 45
FIG 44— Marcasite Crystal with °oP,no(w), oP,ooi(c), P^o , on (/) and JPS5 ,
013 (T»)
FIG 45 — Marcasite Crystal with Forms as Indicated in Fig 44, and P M , 101 (e)
and P, in (s)
andP <56 (on) The other forms observed on most crystals are oo P(iio),
P(III), and often |P oo (013)
Twins are very common, with oo P(no) the twinning plane (Fig 46)
Sometimes these are aggregated by repeated twinning into serrated
groups known as cockscomb twins or spearhead twins (Fig 47), because
FIG 46 FIG 47
FIG 46 —Twin of Marcasite about oo P(iio)
FIG 47 — Spearhead Group of Marcasite Fourling Twinned about no and then
about i To
of the outlines of their edges. In many instances the crystals aie acic-
ular or columnar in habit, forming radiating groups with globular, rem-
form and stalactitic shapes Concretions are also common The basal
plane is usually striated parallel to the edge between it and P oo (on)
The cleavage is distinct parallel to oo P(iio) The fracture is uneven
SULPHIDES, TELLURIDES, ETC. Ill
When powdered marcasite is treated \\ith cold nitric acid and
allowed to stand, it decomposes \uth the separation of sulphur
Marcasite readih alters to limonite The fact that pyrite, sphaler-
ite, chalcopyrite, and other minerals form pseudomorphs after it
indicates that, under suitable conditions, it alters also to these com-
pounds The mineral is in most cases a direct result of precipitation
from hot solutions
Synthesis — Marcasite crystals ha\e been prepared by the reduction
of FeSQi by charcoal in an atmosphere of EfeS
Occurrence ani Uses — The mineral, like pyrite, is found embedded
in rocks in the form of crystals and concretions, and also as the
gangue masses of veins It constitutes nearly the entire filling of some
veins, and forms druses on the walls of cavities in both rocks and miner-
als It also replaces the organic matter of fossils preserving their shapes
— thus producing true pseudomorphs
When associated \\ith pyrite it is mined together \\ith this mineral
as a source of sulphur
Localities — Crystalline marcasite occurs m such great quantity
near Carlsbad m Bohemia that it is mined The cockscomb variety is
found in Derbyshire, England, and crystals at Schemmtz in Hungary
and at Andreasberg and other places in the Harz In the United States
the mineral occurs as crystals at a great number of places, being par-
ticularly abundant m the lead and zinc localities of the Mississippi
Valley, where it sometimes forms stalactites The stalactites from
Galena, 111 , often consist of concentric layers of sphalerite, galena and
crystallized marcasite
Arsenopyrite (FeAsS)
Arsenopyrite, or mispickel, is the most important ore of arsenic
It is found in crystals and in compact and granular masses. It is a
silver-white metallic mineral resembling very closely cobaltite in its
general appearance
The formula FeAsS for arsenopynte is based on analyses like the
following.
As S Fe Total
Specimen from Hohenstein, Saxony 45 62 19 76 34 64 100 02
Specimen from Mte Chalanches, France 45 78 ig 56 34 64 99 98
Theoretically, the mineral consists of its components m the following
proportions, As 46 per cent, S 19 7 per cent, Fe 34 3 per cent In many
specimens the iron is replaced in part by cobalt, nickel or manganese.
112
DESCRIPTIVE MINERALOGY
Sometimes the cobalt is present in such large quantity that the mineral
is smelted as an ore of this metal
The axial ratio of arsenopynte is 6773 i i 1882 Its crystals are
usually simpler than those of marcasite (Fig 48), though the number of
planes observed in the species is larger. Most of the untwmned crystals
are a combination of oo P(no)
with JP66 (014), or P 06 (on),
or POO(IOI), and have a pris-
matic habit. Twins are not
rare The twinning plane is
the same as in marcasite,
and repetition is often met
with The angle no/\i"io=
68° 13'
FIG 48-Arsenopynte Crystals with cop, The brachydomes are stri-
no (m) , iP oo , 014 (M), and P 5 , on (j) ated horizontally, and often
the planes ooP(no) are stri-
ated parallel to the edge oo P(no) A? *> (101)
The cleavage of arsenopynte is quite perfect parallel to ooP(no)
The mineral is brittle and its fracture uneven Its hardness is 5 5-6
and density about 6 2 Its color is silver-white to steel-gray, its streak
grayish black It is a good conductor of electricity
In the closed tube arsenopynte at first gives a red sublimate of AsS
and then a black mirror of arsenic On charcoal it gives the usual
reactions for sulphur and arsenic Cobaltiferous varieties react for
cobalt with borax. The mineral yields sparks when struck wilh. steel
and emits an arsenic smell It dissolves m nitric acid with the separa-
tion of sulphur
Arsenopynte is distinguished from the cobalt sulphides and arsenides
by the absence of Co
Synthesis — Crystals of the mineral are produced by heating in a
closed tube at 300° precipitated FeAsS in a solution of NaHCO*
Occurrence — Arsenopynte crystals are often found disseminated
through crystalline rocks, and often embedded m the gangue minerals of
veins Like pyrite and marcasite they frequently fill vein fissures. Its
associates are silver, tin and lead ores, chalcopyrite, pynte and sphalerite
Localities — The mineral is abundant at Freiberg, m Saxony, at
Tunaberg, in Sweden, and at Inquisivi Mt , Sorato, m Bolivia
It also occurs in fine crystals at Francoma in New Hampshire, at
Blue Hill m Maine, at Chatham in Connecticut, and at St. Francois,
Beauce Co, Quebec Massive arsenopynte is found near Kecscville
SULPHIDES, TELLURIDES ETC 113
Essex Co , near Edenville, Orange Co , and near Carmel, Putnam Co ,
N Y , and at Re\\ald, Flo\d Co , Va In most cases it is appaiently
a result of pneumatoh sis
Uses — Arsenopynte was formerly the source of nearly all the arsenic
of commerce The mineral is concentrated b\ mechanical methods, and
the concentrates are heated in retorts, when the following reaction takes
place FeAsS = FeS+As The arsenic being volatile is conducted
into condensing chambers where it is collected When the mineral con-
tains a reasonable amount of cobalt or of gold these metals are extracted
Uses of Arsenic — The metal arsenic has \ery little use in the arts,
though its compounds find many applications as insecticides, medicines,
pigments, in tanning, etc The basis of most of these is AsoOs, and
this is produced directly from the fumes of smelters working on arsenical
gold, silver and copper ores Only a portion of such fumes are saved,
however, as even half of those produced at a single smelter center
(Butte, Montana), would more than supply the entire demand of the
United States for arsenic and its compounds Under these conditions
the mining of arsenical pynte as a source of arsenic has ceased so far
as the United States is concerned
Lollingite (FeAso) is usually massive, though its rare crystals are
isomorphous in e\ery respect with those of arsenopynte The pure
mineral is not common Most specimens are mixtures of lollmgite with
arsenopynte or other sulphides or arsenides.
The mineral is silver-white or steel-gray Its streak is grayish black
Its hardness is 5-5 5 and density about 72 It readily fuses to a mag-
netic globule, at the same time evolving arsenic fumes It is soluble in
HN03
It usually occurs in veins associated with other sulphides and arsen-
ides It is found at Pans, Maine; at Edenville and Monroe, N. Y.;
at vanous mines in North Carolina, and on Brush Creek, Gunnison
Co., Colo At the last-named locality the mineral is in star-shaped
crystalline aggregates, in twins and trillings, associated with siderite
and barite.
SYLVANITE GROUP
The sylvanite group includes at least three distinct minerals, all of
which are ditellurides of gold or silver. The group is isodunorphous.
The pure gold tellunde is known only in monochmc crystals, but the
isomorphous mixtures of the gold and silver compounds occur both in
monochmc and orthorhombic crystals
114 DESCRIPTIVE MINERALOGY
Orthorhombic bipyramidal Monoclmic prismatic
AuTeo Calavente
Krennente (Ag Au)Te2 Syhamte
All three minerals are utilized as ores of gold While occurring only
in a few places, they are sufficiently abundant at some to be mined
Calaverite (AuTe2)
Calavente is a nearly pure gold chloride However, it is usually
intermixed with small quantities of the silver tellunde An analysis of a
specimen from Kalgoorhe, Australia, gave Te=5727, Au=4i 37,
Ag=58
Calaverite crystallizes m the monoclmic system (prismatic class) in
crystals that are elongated parallel to the orthoaxis and deeply striated
in this direction. Their axial ratio is i 6313 i ' i 1449 with £=90° 13'
The prominent forms are ooP 66(100), ooP«D(oio), oP(ooi),
-Poc(ioi), +P6o(ioT), -2Poo(20i), +2P66(2oT), and P(in)
Twinnmg is common and the resulting tuiins are very complicated
Usually, however, the mineral occurs massive and granular
Calavente is opaque, silver-white or bronzy yellow in color and has a
yellow-gray or greenish gray streak. Its surface is frequently covered
with a yellow tarnish. The mineral is brittle and without distinct cleav-
age Its hardness is 2-3 and density 9 04
On charcoal before the blowpipe the mineral fuses easily to a yellow
globule of gold, yielding at the same tune the fumes of tellurium oxide.
It dissolves in concentrated EfeSO.*, producing a deep red solution. When
treated with HNOs it decomposes, leaving a rusty mass of spongy gold
The solution treated with HC1 usually yields a slight precipitate of silver
chloride
Calaverite is distinguished from most other minerals by the test for
tellurium It is distinguished from fetzite (p 80), by its crystallization
and the fact that it gives a yellow globule when roasted on charcoal,
and from sylvamte by the small amount of silver it contains, its higher
specific gravity, its color and its lack of cleavage It is distinguished
from krennente by its crystallization
Occurrence — The mineral occurs in veins with the other tellurides
associated with gold ores in Calaveras Co , Cal , and at the localities
mentioned for petzite (see p 81) It is believed to have been deposited
by pneumatolytic processes or by ascending magmatic water at com-
paratively low temperatures.
SULPHIDES, TELLURIDE8, ETC 115
Uses. — The mineral is mined with other tellundes in Boulder Co ,
and at Cripple Creek, Colorado, as an ore of gold
Sylvamte (Ag Au)Te2
Sylvamte is more common than calavente It is an isomorphous
mixture of gold and silver tellundes in the ratio of about i . i Analyses
follow
I Te=62 16 Au=24 45 Ag=i3 39 Total=ioo oo
II Te=59 78 Au=26 36 Ag = i3 86 " ico oo
III Te=58 91 Au=29 35 Ag=n 74 k* 100 oo
I Theoretical for AgTe2+ \uTe2
II and III Specimens trom Boulder Co , Colo
In crystallization the mineral is isomorphous with calavente, with
an axial ratio a b . c= i 6339 i : i 1265 and $=90° 25' Its crystals
are usually rich in planes, about 75 ha\mg been identified Their habit
is usually tabular parallel to ooP ob (GIO), with this plane, —P 5c (101),
oP(ooi), oo P 5b (100) and 2P2(T2i) predominating The mineral also
occurs in skeleton crystals and in aggregates that are platy or granular
Twinning is common, \\ith — P<X(IOI) the twinning plane Many
twinned aggregates form networks suggesting writing, hence the name
" Schnfterz '' often applied to the mineral by the Germans
Sylvamte is silver-white or steel-gray and has a brilliant metallic
luster and a silver-white or yellowish gray streak Its hardness is
between i and 2 and its densiU 7 9-8 3 Moreover, it possesses a per-
fect cleavage parallel to oo P ob (oio)
Its chemical properties are the same as those of calavente, but the
silver precipitate produced by adding HC1 to its solution m HNOs is
always large It is best distinguished from the gold tellunde by its
cleavage and from fetzite ((AgAu^Te) and lessite (AgsTe) by its
crystallization, and by the yellow metallic globule produced when the
mineral is roasted on charcoal It is distinguishable from krennente by
its crystallization
Localities and Origin — Sylvanite occurs with the other tellundes in
veins at Offenbanya and Nagyag in Transylvania, at Cripple Creek and
m Boulder Co , Colo , near Kalgoorhe, W Australia, in small quan-
tities near Balmoral in the Black Hills, S D , and at Moss, near Thunder
Bay, Ontano Like calavente it TV as deposited by magmatic water, or
by hot vapors
Uses — It is mined with calaverite as a gold and silver ore at Cripple
Creek and in Boulder Co , Colo.
CHAPTER V
THE SULPHO-SALTS AND SULPHO-FERRITES
THE sulpho-salts are salts of acids analogous to arsenic acid,
and arsenious acid, HsAsOs, and the corresponding antimony acids
HsSb04 and EfeSbOs The sulpho-acids differ from the arsenic and the
antimony acids in containing sulphur in place of oxygen, thus HsAsS-i,
HsAsSa, H3SbS4 and H3SbS3. The mineral enargite may be regarded as
a salt of sulpharsenic acid, thus CusAsS-i, copper having replaced the
hydrogen of the acid Proustite, on the other hand, is AgsAsSs, or a
salt of sulpharsemous acid. The salts of sulpharsenic acid are called
sulpharsenates, while those derived from sulpharsemous acid are known
as sulpharsemtes The sulpharsenates are not represented among the
commoner minerals, although the copper salt enargite is abundant at a
few places A number of salts of other sulphur-arsenic acids are known
but they are comparatively rare
There is another class of compounds with compositions analogous
to those of the sulpho-salts, though their chemical nature is not well
understood This is the group of the sulpho-ferntes We know that
certain hydro-sides of iron may act as acids under certain conditions
The sulpho-ferrites may be looked upon as salts of these acids in which,
however, the oxygen has been replaced by sulphur, as in the case of the
sulpho-acids referred to above Thus by replacement of 0 by S, m
feme hydroxide Fe(OH)s the compound Fe(SH)s or HsFeSs results
The salts of this acid are sulpho-ferrites This acid, by loss of HaS,
may give rise to other acids in the same way that sulphuric acid (EfeSO/O,
by loss of HaO, gives nse to pyrosulphuric acid In the case of the
sulpho-acid we may have HsFeSs— H2S=HFeS2 The copper salt of
this acid is the common mineral chalcopyrite, CuFeS2
The sulpho-salts are very numerous, but only a few of them are of
sufficient importance to warrant a description in this book
116
SULPHO-SALTB AND SULPHO-FERRITES 117
THE SULPHARSENITES AND SULPHANTIMONITES
The sulpharsemtes and sulphantimomtes are denvatives of the
ortho acids HsAsSs and
ORTHO SULPHO-SALTS
The ortho salts are compounds in \\hich the hydrogen of the ortho
acids is replaced by metals They include a large number of minerals,
of which the following are the most important.
Boitrnomte (Cus Pb)s (SbSs)2 Orthorhombic
Pyrargynte AgsSbSa Hexagonal
Proustite AgsAsSs Hexagonal
PYRARGYRITE GROUP
Pyrargynte (AgsSbSs)
Pyrargyrite, or dark ruby silver, is an important silver ore, especially
in Mexico, Chile and the \\estern United States. The name ruby silver
is given to it because thin splinters transmit deep red light The mineral
is usually mixed with other ores in compact masses, but it also forms
handsome crystals
The composition of pyrargyrite is represented by the formula AggSbSs
which demands 17 82 per cent S , 22 21 per cent Sb , 59 97 per cent Ag
Many specimens contain also a small quantity of arsenic, through the
admixture of the isomorphous compound proustite The analyses given
below show the effect of the intermixture of the two molecules
S Sb As Ag Total
Andreasberg, Harz 17 65 22 36 59 73 99 77
Zacatecas, Mexico 17 74 22 39 27 60 04 100 44
Freiberg, Saxony 17 95 18 58 2 62 60 63 99 78
The crystals of pyrargyrite are rhombohedral and hemunorphic
(ditngonal pyramidal class), with an axial ratio i : 8038 They are
usually quite complex and are often twinned. The species is very rich
in forms, not less than 150 having been reported The most prominent
of these are ooP2(ii2o), ooP(ioTo), R(ioli), -iR(oil2) and the
scalenohedrons R3(2i3i) and iR3(2i34) (Fig ^49) In the commonest
twinning law the twinning plane is ooP2(ii2o) and the composition
118 DESCRIPTIVE MINERALOGY
face oPfooi) The c axes in the twinned portions are parallel and the
o=P2(ii2~o) planes coincident, so that the t\\m at a hasty glance looks
like a simple crystal The angle roll /\lioi = 71° 22'
The cleavage of pyrargynte is distinct parallel to R(ioTi) Its frac-
ture is conchoidal or une\ en The mineral is apparently opaque and its
color is grayish black in reflected light, but is trans-
parent or translucent and deep red in transmitted
light Its streak is purplish red For lithium
light 03=3084, €=2881 It is not an electrical
conductor
In the closed tube the mineral fuses easily and
/
ghes a reddish sublimate When heated
^ sodium carbonate on charcoal it is reduced to a
P\ra^g\nte * with g^°bule of silver, \vhich, when dissolved in nitric
1 1 20 (a) acid, yields a silver chloride precipitate when
I treated \\ith a soluble chloride The mineral dis-
solves in nitric acid with the separation of sulphur
and a white precipitate of antimony oxide It is also soluble in a
strong solution of KOH From this solution HC1 precipitates orange
Sb2Ss (compare proustite)
The color and streak of p>rargynte, together with its translucency,
distinguish it from nearly all other minerals Its reaction for silver
serves to distinguish it from cuprite, dnnalar and realgar, which it some-
times resembles The distinction between this mineral and its iso-
morph, proustite, is based on the streak and the reaction for anti-
mony.
Pyrargynte occurs as a pseudomorph after native silver. On the
other hand it is occasionally altered to pynte or argentite, and some-
times to silver
Syntheses — Microscopic crystals ha\e been made by heating in a
porcelain tube, metallic silver and antimony chlorides in a current of
IfeS, and by the action of the same gas at a red heat on a mixture of
metallic silver and melted antimony* o\ide
Occurrence, Localities and Origin — Pyrargynte occurs in veins asso-
ciated with other compounds of silver and scmetimes with galena and
arsenic It is most common in the zone of secondary enrichment of
silver veins. The crystallized variety is found at Andreasberg in the
Harz, at Freiberg, in Saxony, at Pnbram, in Bohemia, at many places
in Hungary, and at Chanarcillo, in Chile The massive variety is worked
as an ore of silver at Guanajuato in Mexico and in several of the western
states, as, for instance in the Ruby district, Gunmson Co , and in other
SULPHO-SALTS AND SULPHO-FERRITES 119
mining districts m Colorado, near Washoe and Austin, Nevada, and at
several points in Idaho, Ne\v Mexico, Utah and Arizona
Uses — The mineral is an important ore of silver in Mexico and in
the western United States It is usually associated with other sulphur-
bearing ores of sil\er, the metal being extracted from the mixture by
the processes referred to under argentite,
Proustite (AgsAsSs)
Proustite, or light ruby siher, is isomorphous with p\rargynte It
differs from the latter mineral in containing arsenic m place of antimony
It occurs both massive and in crystals, and like pyrargynte is an ore of
silver
The formula abo\e given demands 19 43 per cent S, 15 17 per cent
As, and 65 40 per cent sih er The analysis of a specimen from Mexico
yields figures that correspond \ery nearly to these Cr}stals from
Chanarcillo contain a slight admixture of the antimony compound
S As Sb Ag Total
Mexico 19 52 14 98 65 39 99 89
Chanarcillo, Chile 19 64 13 85 i 41 65 06 99 96
Like pyrargynte, proustite is rhombohedral Its crystals are pris-
matic or acute rhombohedral The forms present on them are much
less numerous than those on the corresponding
antimony compound, the predominant ones being
ocp2(ii2o), iR(ioT4), -iR(oil2), Rd(2i3i),
~|R4(3557J and other scalenohedrons (see Fig
50) Twins are common, the t winning planes
being (i), parallel to JR(iol4) and (2) parallel to
R(ioTi) The angle io7i Alici = 7i° 12'. FlG So-Crystal of
The cleavage, fracture and haidness of prous- JJJHJ ^ * Jj
tite are the same as for pyrargynte Its hard- (j/) and -|R, 0112 («).
ness is 2 and its density is about 5.6 The mineral
is transparent or translucent Its color is grayish black by reflected
light and scarlet m transparent pieces by transmitted light. Under the
long-continued influence of daylight the color deepens until it becomes
darker than that of pyrargynte Its streak is cirnabar-red to brownish
black Its luster is adamantine. It is a nonconductor of electncity
For sodium light 03=3 0877, €= 2 7924
In the closed tube proustite fuses easily and gives a slight sublimate
120 DESCRIPTIVE MINERALOGY
of \\hite arsenic oxide In its other chemical properties it resembles
pyrargyrite except that it gi\es reactions for arsenic \\here this mineral
reacts for antimony, and yields onh sulphur \\hen dissohed in HNOa
From its solution in KOH a yellow precipitate of As^Ss is thrown do\\n
upon the addition of HC1 (compare pyrargyrite)
Proustite differs from pyra g \nte in Us color, transparency and
streak, as \vell as in its arsenic reactions It is distinguished from
cinnabar and cuprite (CuO) b> the arsenic test
Syntheses — Crystals of proustite ha\e been produced by reactions
analogous to those that yield p\rargynte, when arsenic compounds are
employed in place of antimon\ compounds
Occurrence — The mineral occurs under the same conditions and with
the same associates as pyrargyrite and it yields the same alteration
products as pyrargynte
Localities and Uses — Handsome crystals of proustite occur at
Freiberg and other places in Saxony, at Wolfach in Baden, at Markirchen
in Alsace and at Chanarcillo in Chile It is associated with pyrargyrite
and with other ores of silver
In the western United States it is quite abundant, more particular!}
in the Ruby district, Colorado, at Poorman lode in Idaho, and in all other
localities where pyrargynte occurs In many it is mined as an ore of
silver
Bournonite ((Pb Cu2)3(SbS3)2)
Bournomte is a comparatively rare mineral It occurs either in
compact or granular masses or in well developed crystals of a steel
gray color It is not of any economic importance except as it may be
mixed with other copper compounds exploited for copper
Analyses of bournomte from two localities are given below
S Sb
I- 19 36 23 57
n. 19 78 23 80
I Liskeard, Cornwall, England
II Felsobinya, Hungary
These analyses are by no means accurate, but they show the compo-
sition of the mineral to be approximately Pb, Cu, Sb and S, in which the
elements are combined in the following proportions 8=19 8 per cent,
Sb=24 7 per cent, Pb 42 5 per cent, Cu 13 per cent
Bournonite crystals are orthorhombic (rhombic bipyramidal class),
As
Pb
Cu
Fe
Total
47
4i 95
13 27
68
99 30
-
42 07
12 82
20
98 67
SULPHO-SALTS AXD 3ULPHOFERRITES
121
with a . b c= 9380 i 8969 They are usually tabular 'Fig 51;, or
short, prismatic in habit, and are often in repeated twins fFig 52*, with
wheel-shaped or cross-like forms The principal planes observed on
them are oP(ooi),P<^(ioij, POD (011 ),iP(ii2), wP(noi, xPxiioo,
and oo P oc (oio), though 90 or more planes are kno\\ n The most com-
mon twinning plane is oo P(no) Angle IIOAIIO— 86° 20'
The luster of the mineral is brilliant metallic Its cclcr and streak
are steel-gray Its cleavage is imperfect, parallel to QC P c£ f oio; and its
fracture conchoidal or uneven Its hardness is 2 5-3 and density 5 8
Like most other metallic minerals it is opaque It is a \ ery poor con-
ductor of electricity
In the closed tube bournomte decrepitates and yields a dark red sub-
limate In the open tube, and on charcoal, it gives reactions for Sb, S,
Pb and Cu When treated with nitric acid it decomposes, producing a
FIG 51 FIG s-
FIG 51 — Bournomte Crystal \uth oP ooi (c], P 55 , 101 (0), \P 112 fu) and P x,
on in)
FIG 52 — Bournonite Fourlmg Tuinned about x P, no (m) Form c same as in
Fig 51 b = =c P oo (oio; and a *= oc P 55 s 100)
blue solution of copper nitrate that turns to an intense azure blue when
an excess of ammonia is added In this solution is a residue of sulphur
and a white precipitate that contains lead and antimon\ .
Bournomte is distinguished from most other minerals by its reactions
for both antimony and sulphur. From other sulphantunonites it is
distinguished by its color, hardness and density.
On long exposure to the atmosphere bournomte alters to the car-
bonates of lead (cerussitej and copper (malachite and azunte)
Synthesis — Crystals of bournomte have been obtained by the action
of gaseous HkS on the chlorides and oxides of Pb, Cu and Sb, at moderate
temperatures
Occurrence — The mineral occurs principally in veins with galena,
sphalerite, stibmte, chalcopynte and tetrahednte
Localities. — Good crystals are found in the mines at Neudorf, Harz;
at Pnbram, m Bohemia, at Felsobanya, Kapnik and other places
in Hungary, and at various places in Chile. In North America it has
122 DESCRIPTIVE MINERALOGY
been found at the Boggs Mine in Yavapai Co , Ariz , in Montgomery
Co , Ark , and at Marmora, Hastings Co , and Darling, Lanark Co ,
Ontario.
THE SULPHDIARSENITES AND SULPHDIANTIMONITES
A large number of sulpho-salts are apparent!} salts of acids that
contain two or more atoms of As or Sb in the molecule These acids
may be regarded as derived from the ortho aads by the abstraction of
HsS, thus The arsemous acid containing two atoms of As may be
thought of as 2H3AsS3-H2S=H4As2S5 Acids with larger proportions
of arsenic may be regarded as derived in a similar manner from three or
more molecules of the ortho acid Only a few of these salts are common
as minerals. Among the more common are two that are lead salts of
derivatives of sulpharsemous and sulphantimonous acids,
Jamesomte (PbsSbgSs) and Dufrenoysite (Pb2AsgS5)
Jamesonite and dufrenoysite are lead salts of the acids H4Sb2Ss and
H4As2Ss Both minerals occur in acicular and columnar orthorhombic
crystals and in fibrous and compact masses of lead-gray color Their
cleavage is parallel to the base The minerals are brittle and have an
uneven to conchoidal fracture Their hardness is 2-3 and density
5 5-6 The streak of jamesomte is grayish black, and of dufreynosite
reddish brown. Both minerals are easily fusible They are soluble in
HC1 with the evolution of EfeS, giving a solution from which acicular
crystals of PbCfe separate on cooling They are decomposed by HNOs,
with the separation of a white basic lead salt They are found in veins
with antimony and sulphide ores abroad and at several points in Nevada
and in the antimony mines in Sevier Co , Arkansas
THE SDLPHARSEWATES AND SDLPHANTIMOITATES
The sulpharsenates are salts of sulpharsenic acid, HaAsS^ and the
sulphantimonates, the salts of the corresponding antimony acid, HsSbS^
These compounds are much less numerous among the minerals than the
sulpharsenites and sulphantimomtes. Moreover, no member of the
former groups is as common as several of the members of the latter
The most important member is the mineral enargite (CusAsS^ an ortho-
sulpharsenate, which in a few places is wrought as a copper ore.
SULPHO-SALTS AND SULPHO-FERRITES 123
Enargite
Enargite, though a rare mineral, is so abundant at a few points that
it has been mined as an ore of copper
Theoretically, the mineral is 8=326, As=i9i, 01=483 Most
specimens, however, contain an admixture of the isomorphous anti-
mony compound, jamaiimte^ and consequently sho\v the presence of
antimony. A specimen from the Rarus Mine, Butte, Montana, yielded
S As Sb Cu Fe Zn Ins Total
31 44 17 91 i 76 48 67 .33 10 ii 100 32
The mineral crystallizes in the orthorhombic system (bipyramidal
class), m crystals with an axial ratio 8694 : i : 8308 Their habit is
usually prismatic, and they are strongly striated
vertically. The crystals are usually highly modi-
fied, with the following forms predominating
oo P 06(100), ooP(no), ooP3(i2o), ooP^f^o),
oo P 06 (oio), and oP(ooi) (Fig 53) Stellar trill-
ings, with ooP2(i2o) the twinning plane, have a
pseudohexagonal habit. The mineral occurs also
in columnar and platy masses FIG ^ _Enarglte Crys_
Enargite possesses a perfect prismatic cleavage tal wth M Pj 1IO (m^
and an uneven fracture. It is opaque with a OOP 55,100 (a), «>pr,
grayish black color and streak. Its hardness is 3 i2o(A)andoP,oor(c).
and density 44. It is a poor electrical conductor.
It is easily fusible before the blowpipe When roasted on charcoal
it gives the reactions for S and As, and the roasted residue when
moistened with HC1 imparts to the flame the azure-blue color char-
acteristic of copper. In the closed tube it decrepitates and gives a
sublimate of S. When heated to fusion it yields a sublimate of arsenic
sulphide The mineral is soluble in aqua regia
Enargite is easily recognized by its crystallization and blowpipe
reactions
Occuiience. — Enargite is associated with other copper ores in veins
filled by magmatiC water at intermediate depths and in a few replace-
ment deposits
Localities — Although not widely distributed, enargite occurs in large
quantities in the copper mines near Morococha, Peru; Copiap6, Chile;
in the province of La Rioja, Argentine; on Luzon, Philippine Islands,
124 DESCRIPTIVE MINERALOGY
and in the United States, at Butte, Montana in the San Juan Moun-
tains, Colorado and m the Tmtic District, Utah
Uses —It is smelted as an ore of copper At the Butte smelter it
furnishes the arsenic that is separated from the smelter fumes and placed
upon the market as arsenic oxide (see p 113)
THE BASIC SULPHO-SALTS
The basic sulpho-salts are compounds in \\hich there is a greater
percentage of the basic elements (metals, etc), present than is
necessary to replace all the hydrogen of the ortho acids Thus, the
copper orthosulpharsenate, enargite, is CusAsSU The mineral steph-
anite is AgsSbS* and the pure silver polybasite AggSbSe
Since three atoms of Ag are sufficient to replace all the hydrogen
atoms m the normal acid containing one atom of antimony and the
quantities of silver present in stephamte and polybasite are in excess
of this requirement, the two minerals are described as basic The
exact relations of the atoms to one another in the molecules are
not known
Although the number of basic sulpho-salts occurring as minerals is
large only four are common These are:
Stephamte AgoSbS* Orthorhombic
Polybasite (Ag - Cu^SbSc Monoclimc
Tetrahednte (R")4Sb2S7 Isometric
T&nnantite (R'^AsoS? Isometric
Stephanite (Ag5SbS4)
Stephanite, though a comparatively rare mineral, is an important ore
of silver in some camps It occurs massive, in disseminated grains and
as aggregates of small crystals Analyses indicate a composition very
dose to the requirements of the formula AgsSbS4
S Sb Ag AsandCu Total
Theoretical . . . 16 28 15 22 68 50 100 oo
Crystals, Chanarollo, Chile 16 02 15 22 68 65 tr 99 89
Stephanite crystallizes in hemimorphic orthorhombic crystals (rhom-
bic pyramidal class), with an axial ratio .6291 : i : .6851. The crystals
are highly modified, 125 forms having been identified upon them. They
have usually the habit of hexagonal prisms, their predominant planes
SULPHO-SALTS AND SULPHO-FERRITES 125
being ooP(no) and oop 06(010), terminated by oP(ooi), P(in) and
2Poc (021) at one or the other end of the c aus (Fig 54) Twins are
common, with oo P(no) and oP(ooi) the t\\ inning planes
The mineral is black and opaque and its streak is black Its hard-
ness is 2 and density =6 2 — 63 It cleaves
parallel to oo P 06 (oio) has an uneven frac-
ture, and is a poor conductor of electricity
On charcoal stephamte fuses \ery easily
to a dark gray globule, at the same time
yielding the \vhite fumes of antimony oxide FIG. 54 —Stephanite Crystal
and the pungent odor of S02 Under the *»th oP, oox («), <*?£,
reducing flame the globule is reduced to oio(ft) ooP, !io W, |P,
,, , m-, i T t - S32 (P)> "°° » °21 W-
metallic silver. The mineral dissolves in
dilute nitric acid and this solution gives a white precipitate with HC1.
Stephamte is easily distinguished from other black minerals by its
easy fusibility, its crystallization, and its reactions for Ag, Sb and S
Localities — The mineral is associated Tvith other silver ores in the
zone of secondary enrichment of veins at Freiberg, Saxony, Joachimsthal
and Pribram, Bohemia, the Comstock Lode and other mines in the
Rocky Mountain region and at many points in Mexico and Peru.
Uses — It is mined together with other compounds as an ore of silver
It is particularly abundant in the ores of the Comstock Lode, Nev., and
of the Las Chispas Mine, Sonora, Mex.
Polybasite ((Ag-Cu)9SbS6)
Polybasite is the name usually applied to the mixture of basic sulph-
ai^fomtes and sulpharsemtes of the general formula R^Sb-AsJSe, in
which R'= Ag and Cu. More properly the name is applied to the anti-
monite, and the corresponding arsenite is designated as pearceite. Sev-
eral typical analyses follow
S As Sb Ag Cu Fe Pb Ins Total
I 17 46 7 56 . . 59 22 15 65 - 99 89
H- 17 7i 7 39 • SS-I7 *S ii i 05 42 99 85
HI. 15 43 5° 10.64 68 39 $ 13 . . 100 09
IV. 16 37 3 88 5 is 6793 607 . .76 ... 100.18
I Pearceite Veta Rica Mine, Sierra Mojada, Mexico
II. Crystals of pearceite, Drumlummon Mine, Marysville, Montana.
III. Polybasite, Santa Lucia Mine, Guanajuato, Mexico
IV. Polybasite, Quespisiza, Clule
126 DESCRIPTIVE MIXERALOGY
The crystallization of the two minerals, which are completely isomor-
phous, is monoclinic (prismatic class) Their axial ratios are
Pearceite, a : b : c= 1.7309 : i : i 6199 £=9°° 9'
Polybasite, =i 7309 : i : i 5796 £=90'
Y
o
The crystals are commonly tabular or prismatic, with a distinct
hexagonal habit. The prominent forms are oP(ooi), P(ni) and
2P 55 (20!). Contact twinning is common, with oo P(no) the twinning
plane, and oP(ooT) the composition plane
Both minerals are nearly opaque Except in very thin splinters
they are steel-gray to iron-black in color Very thin plates are trans-
lucsnt and cherry-red Their streaks are black Their cleavage is
perfect parallel to oP(ooi) and their fracture uneven Their hardness
is 2-3, and density 6-6 2
Both minerals are easily fusible They usually exhibit the reactions
for Ag, Sb, As and S
They are readily distinguished from all other minerals but silver
sulpho-salts by their blowpipe reactions From these they are distin-
guished by their crystallization Pearceite and polybasite are distin-
guished from one another by the relative quantities of As and Sb they
contain
Occurrence — Both minerals occur in the zone of secondary enrich-
ment in veins of silver sulphides.
Localities — Polybasite was an important ore of silver in the Comstock
Lode, Nevada It is at present mined with other silver ores at Ouray,
Colorado, at Marysville, Montana, at Guanajuato, Mexico, and at
various points in Chile Good crystals occur at Freiberg, Saxony, at
Joachimsthal, Bohemia, and in the mines in Colorado, Mexico and Chile.
TETRAHEDRITE GROUP
The name tetrahedrite is given to a mixture of basic sulphanti-
monites and sulpharsenites crystallizing together in isometric forms with
a distinct tetrahedral habit (hextetrahedral dass) The isomorphism
is so complete that all gradations between the various members of the
group are frequently met with The arsenic-bearing member of the
series is known as tennantite and the corresponding antimony member as
letrakednte The latter is the more common
The following six analyses of tetrahedrite will give some idea of the
great range in composition observed in the species.
SULPHO-SALTS AND St'LPHO-FERRITES 127
S Sb As Cu Fe Zn Ag Hg Pb Total
I 27 60 25 87 tr 35 85 2 66 5 15 2 30 99 43
II 23 51 17 21 7 67 42 oo 8 28 49 55 99 71
III. 24 44 27 60 27 41 4 27 2 31 14 54 . 100 57
IV 24 89 30 18 tr 32 80 5 85 07 5 57 99 36
V 21 67 24 72 33 53 56 i So 16 23 98 51
I Xewbur>port, Mass
II Cajabamba, Peru
HI Star City, Xev
IV Poracs, Hungary.
V Arizona.
Upon examination these are found to correspond approximately to
the formula R' ^SbaS:, in which the R" is Cu2, Pb, Fe, Zn, Hg, Ag2 and
sometimes Co and Ni When R is replaced entirely by copper, the
formula (CusSb2S-) demands 23 i per cent S, 24 8 per cent Sb and 52 i
per cent Cu
Analyses of tennantite yield analogous results that may be repre-
sented by the formula CusAs2Sr which demands 26 6 per cent S, 20 76
per cent As and 52 64 per cent Cu
Analyses of even the best crystallized specimens rarely yield As or
Sb alone. Moreover, nearly all show the presence of Zn in notable
quantity The great variation noted in the composition of different
specimens which appear to be pure crystals has led to the proposal of
other formulas than those given abo\e — some being simpler and others
more complex It is possible that the variation may be explained as
due, in part, to some kind of solid solution, rather than as the result
solely of isomorph'jus replacement It is more probable, however, that
it is due to the intergrowth of notable quantities of various sulphides
with the sulpho-salts
There is still considerable confusion in the proper naming of the mem-
bers of the series, but generally the forms composed predominantly of
Cu, Sb and S with or without Zn are known as tetrahednte and those
containing As m place of Sb as tennantite, although several authors
confine the use of the latter term to arsenical tetrahedrites containing a
notable quantity of iron
Since the members of the tetrahedrite series often contain a large
quantity of metals other than Cu and Zn the group has been so sub-
divided as to indicate this fact Thus, there are argentiferous, mercurial
and plumbiferous varieties of tetrahedrite Some of these varieties are
utilized as ores of the metals that replace the copper and zinc in the more
128 DESCRIPTIVE MINERALOGY
common varieties The relations of the ordinary (II) and the bis-
muthiferous tennantites (III) to tetrahednte (I) are shown by the fol-
lowing three analyses.
S As Sb Bi Cu Fe Ag Pb Co Total
I 24 48 tr 28 85 45 39 i 3* " IQo 15
II 26 61 19 03 51 62 i 95 99 21
III 29 10 ii 44 2 19 13 07 37 52 6 51 04 i 20 101 07
I Fresney d'Oisans, France.
II Cornwall, England.
Ill Cremenz, Switzerland
The crystals of both tetrahedrite and tennantite are tetrahedral in
habit, the principal forms on them consisting of the simple tetrahedron
and complex tetrahedrons such as —(211), — — (332) together with
the dodecahedron, ooQ(iio) and the cube, ooOoo(ioo) (Fig. 55)
Twins are common with 0(in) the twinning
plane. These are sometimes contact twins
and sometimes interpenetration twins. Some
crystals are very complicated, because of the
presence on them of a great number of forms
The total number of distinct forms that have
been identified is about 90. The mineral
m L j ^ occurs also in granular, dense and earthy
FIG 55 —Tetrahednte Crys- 6 ' J
o masses.
tal with -, 1 1 1 W , "» o, The fracture of the tetrahedrites is uneven
no (d) and fO, 332 (»). Their hardness varies between 3 and 4 5 and
their density between 4 4 and 5 i Their color
is between dark gray and iron-black, except in thin splinters, which
sometimes exhibit a cherry-red translucency. Their streak is like their
color. All tetrahedrites are thermo-electric.
The chemical properties of the different varieties of tetrahedntes
vary with the constituents present. All give tests for sulphur and for
either antimony or arsenic, and all show the presence of copper in a
borax bead. The reactions of other metals that may be present may
be learned by consulting pages 483-494.
The crystals of tetrahedrite are so characteristic that there is little
danger of confusing the crystallized mineral with other minerals of the
same color. The massive forms resemble most dearly arseno$yritey
lownmtie and chalcocite From these the tetrahedrites are
SULPHO-SALTS AND SULPHO-FERRITES 129
best distinguished by their hardness, together with their blowpipe reac-
tions
Tetrahednte appears to suffer alteration quite readily, since pseudo-
morphs of several carbonates and sulphides after tetrahednte crystals
are well known
Syntheszs — Crystals of the tetrahedrites have been made by passing
the vapors of the chlorides of the metals and the chlorides of arsenic or
antimony and EfeS through red-hot porcelain tubes They have also
been observed in Roman coins that had Iain for a long time in the hot
springs of Bourbonne-les-Bains, Haute-Marne, France.
Occurrence — The tetrahedrites are very common in the zone of
secondary enrichment of sulphide veins and in impregnations They
occur associated with chalcopyrite, pynte, sphalerite, galena and other
silver, lead and copper ores in nearly all regions where the sulphide ores
of these metals are found They occur also as primary constituents of
veins of silver ores, where they were deposited by magmatic waters.
Localities — In the United States tetrahedrite occurs at the Kellogg
Mines, ten miles north of Little Rock, Arkansas, near Central City and
at Georgetown, Colorado; in the Ruby and other mining districts in
the same State; at the De Soto Mine in Humboldt Co , Nevada, and
at several places in Montana, Utah and Arizona It is found also in
British Columbia and in Mexico, and at Broken Hill, New South Wales
The arsenical tetrahedrites are not quite as common as is the anti-
monial variety Excellent crystals occur in the Cornish Mines, at
Freiberg in Saxony, at Skutterud in Norway, and at Capelton,
Quebec
Uses. — The mineral is used to some extent as an ore of silver or of
copper, the separation of the metals being effected in the same way as
in the case of the sulphides of these substances.
THE SULPHO-FERRITES
Only two sulpho-f emtes are sufficiently important to merit descrip-
tion here Both of these are copper compounds and both are used as
ores of this metal, one — chalcopyrite — being one of the most important
ores of the metal at present worked
The first of these minerals discussed, bornite, is a basic salt of
the acid EfeFeSa, the second is the salt of the derived acid HFeS2,
which may be regarded as the normal acid from which one molecule of
H2S has been abstracted (see p. n6],
130 . DESCRIPTIVE MINERALOGY
Bornite (Cu5FeS4)
Bormte, known also as horseflesh ore because of its peculiar purplish-
red color, is found usually massive In Montana and in Chile it con-
stitutes an important ore of copper
Bornite is probably a basic sulpho-femte, though analyses yield
lesults that vary quite widely, especially in the case of massive varieties
This variation is due to the greater or less admixture of copper sulphides,
mainly chalcocite, with the bormte The theoretical composition of the
mineral is 25 55 S, 63 27 Cu, and 11.18 Fe The analyses of a crystallized
variety from Bristol, Conn , and of a massive variety from the Bruce
Mines, Ontano, follow.
S Cu Fe Ins Total
Bristol, Conn . 25 54 63 24 n 20 99 98
Bruce Mines, Ont 25 39 62 78 n 28 30 99 75
The crystallization of bormte is isometric (hexoctahedral class), in
combinations of oo O oo (ico), oo 0(iio),0(rn), and sometimes 202(211)
Crystals often form mterpenetration twins, with 0 the twinning plane
The fracture of the mineral is conchoidal, its hardness 3 and density
about 5 On fresh fracture the color varies from a copper-red to a pur-
plish brown Upon exposure alteration rapidly takes place covering
the mineral with an iridescent purple tarnish. Its streak is grayish
black It is a good conductor of electricity
Chemically, the mineral possesses no characteristics other than those
to be expected from a compound of iron, copper and sulphur It dis-
solves in nitric acid with the separation of sulphur
It is easily recognized by its purplish brown color on fresh fractures
and its purple tarnish.
Bornite alters to chalcopyrite, chalcocite. covellite, cuprite (CuaO),
chrysocolla (CuSiQs 2H20) and the carbonates, malachite and azurite.
On the other hand, bornite pseudomorphs after chalcopyrite and chal-
cocite are not uncommon
Syntheses — Roman copper coins found immersed in the water of
warm springs in France have been partly changed to bornite. Crystals
have been formed by the action of EkS at a comparatively low tempera-
ture (ioo°-2oo° C ), upon a mixture of CuaO, CuO and Fe20s
Occurrence and Origin — Bornite is usually associated with other
copper ores in veins and lodes, where it is in some cases a primary min-
eral deposited by magmatic waters and in others a secondary mineral
produced in the zone of enrichment of sulphide veins. It also sometimes
SULPHO-SALTS AND SULPHO-FERRITES 131
impregnates sedimentary rocks, where its origin is part due to contact
action.
Localities — The crystallized mineral occurs near Redruth, Cornwall
Eng , and at Bristol, Conn The massive mineral is found at many
places in Norway and Sweden It is the principal ore of some of the
Bolivian, Chilian, Peruvian and Mexican mines and of the Canadian
mines near Quebec In the United States it has been mined at
Bristol, Conn , and at Butte, Montana
Uses — Bornite is mined with chalcopyrite and other copper com-
pounds as an ore of this metal
Chalcopynte (CuFeS2)
From an economic point of \ie\\ this mineral is the most important
of the sulpho-salts, as it is one of the most important ores of copper
FIG 56 FIG 57 FIG 58
FIG. 56 —Chalcopynte Crystal with P, in (p), -P, ill (p) and 2? x> , 201 (3).
IP Pz
FEG 57 — Chalcopynte Crystal with — , 772 (&J and — , 212 (x) The form ^
2 2
sometimes approaches « P(zio) and x approaches P *s (xoi1)
FIG 58 — Chalcopynte Twinned about P(iu)
known. It occurs both massive and crystallized. From its similarity
to pyrite in appearance it is often known as copper pyrites.
Crystallized specimens of chalcopyrite contain 35 per cent S, 34 5
per cent Cu and 30.5 per cent Fe, corresponding to the formula CuFeSk,
i e , a copper salt of the acid HFeS2 The mineral often contains small
quantities of intermixed pyrite. It also contains in some instances
selenium, thallium, gold and silver
The crystallization of chalcopynte is in the sphenoidal, hemihedral
division of the tetragonal system (tetragonal scalenohedron class).
132 DESCRIPTIVE MINERALOGY
P
The crystals are usually sphenoidal in habit with the sphenoids -(in),
3p
and —(332) the predominant forms (Figs 56 and 57) In addition to
2
these there are often present also oo P oo (100), oo P(no), 2? oo (201),
ff
and a very acute sphenoid that is approximately — (772), supposed to be
p
due to the oscillation of oo P(no) and -(in) (Fig 57) Twins are quite
common, with the twinning plane parallel to P (Fig 58). The plus
faces of the sphenoid are often rough and striated, while the minus faces
are smooth and even.
The fracture of the mineral is uneven. Its hardness is 3 5-4 and
density about 4.2. Its luster is metallic and color brass-yellow Old
fracture surfaces are often tarnished with an iridescent coating Its
streak is greenish black. It is an excellent conductor of electricity
On charcoal the mineral melts to a magnetic globule. When mixed
with Na2COs and fused on charcoal, a copper globule containing iron
results. When treated with nitric aad it dissolves, forming a green
solution in which float spongy masses of sulphur The addition of
ammonia to the solution changes it to a deep blue color and at the same
time causes a precipitate of red feme hydroxide.
From the few brassy colored minerals that resemble it, chalcopyrite
is distinguished by its hardness and streak.
When subjected to the action of the atmosphere or to percolating
atmospheric water chalcopyrite loses its iron component and changes
to covelhte and chalcocite The iron passes into limomte. Bornite,
copper and pyrite are also frequent products of its alteration. In the
oxidation zone of veins it yields limonite, the carbonates, malachite and
azurite, and cuprite (Cu20). When exposed to the leaching action of
water, limonite alone may remain to mark the outcrop of veins, the
copper being carried downward in solution to enrich the lower portions
of the vein. The deposit of limonite on the surface is known as
Syntheses — Crystals of chalcopyrite have been produced by the
action of HaS upon a moderately heated mixture of CuO and F^Os
cndosed in a glass tube. The mineral has also been made by the action
of warm spring waters upon ancient copper coins. It is also a fairly
common product of roasting-oven operations
Occurrence and Origin.— Chalcopyrite is widely disseminated as a
primary vein mineral, and is often found in nests in crystalline rocks.
SULPHO-SALTS AND SULPHO-FERRITES 133
It also impregnates slates and other sedimentary rocks, schists and
altered igneous rocks where, in some cases, it is a contact deposit
and in others is original It is also formed by secondary processes caus-
ing enrichment of copper sulphide veins Its most common associ-
ates are galena, sphalerite and pyrite. It is the principal copper ore
m the Cornwall mines, where it is associated with cassitente (Sn02),
galena and other sulphides. It is also the important copper ore of
the deposits of Falun, Sweden, of Namaqualand in South Africa,
those near Copiapo in Chile, those of Mansfeld, Germany, of the Rio
Tinto district in Spain, of Butte and other places in Montana, and of
the great copper-producing districts in Arizona, Utah and Nevada.
Crystals occur near Rossie, Wurtzboro and Edenville, N. Y., at the
French Creek Mines, Chester Co., Penn., near Finksburg, Md., and at
many other places
Extraction — The mineral is concentrated by mechanical methods.
The concentrates are roasted at a moderately high temperature, the iron
being transformed into oxides and the copper partly into oxide and
partly into sulphide. Upon further heating with a flux the iron oxide
unites with this to form a slag and the copper sulphide melts, and collects
at the bottom of the furnace as " matte/' which consists of mixed copper
and copper sulphide. This is roasted in a current of air to free it from
sulphur. By this process all of the copper is transformed into the oxide,
which may be converted into the metal by reduction. The metal is
finally refined by electrical processes. Much of the copper obtained
from chalcopyrite contains silver or gold, or both, which may be recov-
ered by any one of several processes.
Uses.— A large portion of the copper produced in the world is obtained
by the smelting of chalcopyrite and the ores associated with it.
Production.— The world's total product of copper has been referred
to in another place (p. 55). Of this total (2,251,300,000 Ib.) the United
States supplied, in 1912, 1,243,300,000 Ib., of which about 1,000,000,000
Ib. were obtained from sulphide ores. Arizona and Montana produced
the greater portion of this large quantity, the former contributing about
359,000,000 Ib. to the aggregate, and the latter 308,800,000 Ib Out-
side of the United States the most important copper-producing countries
are Mexico, Japan, Spain and Portugal, Australia, Chile, Canada,
Russia, Peru and Germany, in the order named. Practically all of this
copper, except that from Japan and Mexico, is extracted from sulphide
ores.
CHAPTER VI
THE CHLORIDES BROMIDES IODIDES \ND FLUORIDES
THE salts belonging to this group are 'compounds of metals with
hydrochloric (HC1), h>drobromic (HBr), hydnodic (HI) and hydro-
fluoric (HF) acids Only a few are of importance Of these some are
simple chlorides, others are simple fluorides, others are double chlorides
or fluorides (i e cryolite, AlFa^NaF), and others are double hydrox-
ides and chlorides (atacamite)
THE CHLORIDES
The simple chlorides crystallize in the isometric system, but in differ-
ent classes in this system. They comprise salts of the alkalies, K, Na
and NKi, and of silver Of these only three mmerals are of importance,
viz.: sylmte, hahte and cerargynte
Halite (Had)
Halite, or common salt, is the best known and most abundant of the
native chlorides It is a colorless, transparent mineral occurring in
crystals, and in granular and compact masses
Pure halite consists of 39 4 per cent Cl and 60 6 per cent Na The
mineral usually contains as impurities clay, sulphates and organic
substances The several analyses quoted below indicate the nature of
the commonest impurities and their abundance in typical specimens
NaCl CaCl MgCl CaS04 Na2S04 Mg2S04 Clay H20
I 97 35 ... i 01 43 23 30
II. 90 3 „ . 5 oo 2 oo 2 oo 70
III, 98 88 tr tr .79 33
I Stassfurt, Germany.
II Vic, France
III. Petit Anse, La.
The crystallization of halite is isometric (hexoctahedral class), the
principal forms being ooOoo(ioo), 0(iu) and ooO(no) Often the
134
CHLORIDES, FLUORIDES, ETC 135
faces of the forms are hollowed or depressed giving nse to what are called
" hopper crystals " (Fig 59). The mineral occurs also in coarse, gran-
ular aggregates, in lamellar and fibrous masses and in stalactites
Its cleavage is perfect parallel to oo 0 oo (100) Its fracture is con-
choidal Its hardness is 2-2 5 and density about 217 Halite, when
pure, is colorless, but the impurities present often color it red, gray,
yellow or blue The bright blue motthngs obsened in
many specimens are thought to be due to the presence
of colloidal sodium. The mineral is transparent or
translucent and its luster is \itreous. Its streak is
colorless Its saline taste is well known. It is
diathermous and is a nonconductor of electricity. prG 59— Hcpper-
The mineral is plastic under pressure and its plasticity Shaped Cube of
increases with the temperature Its index of refraction Halite
for sodium light, «= i 5442
In the closed tube halite fuses and often it decrepitates. When
heated before the blowpipe it fuses (at 776°) and colors the flame yellow.
The chlorine reaction is easily obtained by adding a small particle cf the
mineral to a microcosmic salt bead that has been saturated with copper
oxide. This, when heated before the blowpipe, colors the flame a bnl-
hant blue. The mineral easily dissolves in water, and its solution yields
an abundant white precipitate with silver nitrate.
The solubility of halite is accountable for a large number of
pseudomorphs. The crystals embedded in clays are gradually dissolved,
leaving a mold that may be filled by other substances, which thus
become pseudomorphs.
Syntheses.— Crystals of halite have been produced by sublimation
from the gases of furnaces, and by crystallization from solution contain-
ing sodium chloride.
Occurrence and Origin —Salt/occurs most abundantly in the water of
the ocean, of certain salt lakes, of brines buned deep within the rocks in
some places, and as beds interstratified with sedimentary rocks. In the
latter case it is associated with sylvite (KC1), anhydrite (CaSO*), gypsum
(CaSO4 2H2O), etc., which, lite the halite, are believed to have been
formed by the drying up of salt lakes or of portions of the ocean that
were cut off from the main IxxLy of water, since the order of occurrence
of the various beds is the sa me as the order of deposition ot the corre-
sponding salts when precipitated by the evaporation of sea water at
varying temperatures (Ojanp pp. 22, 23.)
Below are given figures* showing the composition of the salts in the
water of the ocean, of GF -at Salt Lake, and of the Syracuse, N. Y.» and
136 DESCRIPTIVE MINERALOGY
Michigan artificial brines (produced by forcing water to the buned rock
salt)
NaCl CaCk MgCl2 NaBr KC1 Na2S04 K2S04 CaS04 MgS04
I 77 07 7 86 i 30 3 89 4 63 5 29
II. 79 57 10 oo 6 25 3 60 58
III 95 97 90 69 . 2 54
IV. 91 95 3 19 2 48 2 39
I Atlantic Ocean
II Great Salt Lake
HI New York bnnes
IV Michigan bnnes
Localities —The principal mines of halite, or rock salt, are at Wie-
liczka, Poland, Hall, Tyrol, Stassfuit, Germany, where fine crystals
are found, the Valley of Cardova, Spain, in Cheshire, England and in
the Punjab region of India At Petit Anse in Louisiana, in the vicinity
of Syracuse, N Y , and in the lower peninsula of Michigan thick beds
of the salt are buried in the rocks far beneath the surface Much of the
salt is comparatively pure and needs only to be crushed to become usable
In most cases, however, it is contaminated with clay and other sub-
stances In these cases it must be dissolved in water and recrystallized
before it is sufficiently pure for commercial uses
The best known deposits are at Stassfurt where there is a great thick-
ness of alternating layers of halite, sylvite (KC1), anhydrite, gypsum,
kieseiite (MgSQa-IfeO) and various double chlorides and sulphates of
potassium and magnesium. Although the halite is in far greater quan-
tity than the other salts, nevertheless, the deposit owes most of its value
to the latter, especially the potassium salts (comp. pp. 137, 142)
Uses. — Besides its use in curing meat and fish, salt is employed in
glazing pottery, in enameling, in metallurgical processes, for clearing
oleomargarine, making butter and in the more familiar household oper-
ations. It is also the chief source of sodium compounds.
Production —Most of the salt produced in the United States is ob-
tained directly from rock salt layers by mining or by a process of solu-
tion, in which water is forced down into the buned deposit and then to
the surface as bnne, which is later evaporated by solar or by artificial
heat In the district of Syracuse, N. Y , salt occurs in thick lenses
interbedded with soft shales In eastern Michigan and in Kansas salt
is obtained from buried beds of rock salt, and in Louisiana from great
dome-like plugs covered by sand, day and gravel. Some of the masses
in this State are 1,756 ft. thick.
CHLORIDES, FLUORIDES, ETC 137
The salt production of the United States for 1912 amounted to 33,-
324,000 barrels of 280 Ib each, valued at $9,402,772 Of this quantity
7,091,000 barrels were rock salt
The imports of all grades of salt during the same time were about
1,000,000 barrels and the exports about 440,000 barrels.
Sylvite (KC1)
Sylvite is isometric, like halite, but the etched figures that may be
produced on the faces of its crystals indicate a gyroidal symmetry (pen-
tagonal icositetrahedral class) The habit of the crystals is cubic with
O(ni) and oo O oo (100) predominating.
Pure sylvite contains 47 6 per cent Cl and 52 4 per cent K, but the
mineral usually contains some NaCl and often some of the alkaline sul-
phates.
The physical properties of sylvite are like those of halite, except that
its hardness is 2 and the density i 99 Its melting temperatuie is 738°
and n for sodium light = i 4903
When heated before the blowpipe the mineral imparts a violet tinge
to the flame, which can be detected when masked by the yellow flame of
sodium by viewing it through blue glass Otherwise sylvite and halite
react similarly.
Halite and sylvite are distinguished from other soluble minerals by
the reaction with the bead saturated with copper oxide, and from one
another by the color imparted to the blowpipe flame.
Synthesis — Sylvite crystals have been made by methods analogous
to those employed in syntheses of halite crystals
Occurrence — Sylvite occurs associated with halite, but in distinct
beds, at Stassfurt, Germany, and at Kalusz, Galicia. It has also been
found, together with the sodium compound, incrusting the lavas of
Vesuvius.
Uses. — Sylvite Is an important source of potassium salts, large quan-
tities of which are used in the manufacture of fertilizers,
CERARGYRITE GROUP
The cerargyrite group comprises the chloride, bromide and iodide of
silver. The first two exist as the minerals cerargyrite and bromargyrite,
both of which crystallize in the isometric system. The isometric Agl
exists only above 146°; below this temperature the iodide is hexagonal.
The exhagonal modification occurs as the mineral iodyrite, which, of
course, is not regarded as a member of the cerargyrite group
138 DESCRIPTIVE MINERALOGY
Cerargyrite (AgCl)
Cerargynte, or horn silver, is an important silver ore It is usually
associated with other silver compounds, the mixture being mined and
smelted without separation of the components It is usually recog-
nizable by its waxy, massive character
Silver chloride consists of 24 7 per cent chlorine and 75 3 per cent
silver, but cerargynte often contains, in addition to its essential con-
stituents, some mercury, bromine and occasionally some iodine Crystals
are rare They are isometric (hexoctahedral class), with a cubical habit,
their predominant forms being oo O oo (100), oo 0(no), 0(in), 20(221)
and 202(211) Twins sometimes occur with 0(in) the twinning face
The mineral is sometimes found massive, embedded among other min-
erals, but is more frequently in crusts covering other substances
The fracture of cerargynte is conchoidal The mineral is sectile
Its hardness is i-i 5 and density about 5 5 Its color is grayish, white
or yellow, sometimes colorless. On exposure to light it turns violet-
brown It is transparent to translucent and its streak is white It is a
very poor conductor of electricity Like halite it is diathermous n for
sodium, light = 2 071.
In the closed tube cerargynte fuses without decomposition On
charcoal it yields a metallic globule of silver, and when heated with oxide
of copper m the blowpipe flame it gives the chlorine reaction The min-
eral is insoluble in water and in nitric acid but is soluble in ammonia, and
potassium cyanide. When a particle of the mineral is placed on a
sheet of zinc and moistened with a drop of water, it swells, turns black
and is finally reduced to metallic silver, which, when rubbed by a knife
blade, exhibits the white luster of the metal.
Cerargyrite is easily distinguished from all other minerals, except
the comparatively rare bromide and iodide, by its physical properties and
by the metallic globule which it yields on charcoal
Syntheses.— Crystals of cerargynte have been obtained by the rapid
evaporation of ammoniacal solutions of silver chloride, and by the cooling
of solutions of the chloride in molten silver iodide
Occurrence — The mineral occurs in the upper (oxidized) portions of
veins of argentiferous minerals, where it is associated with native silver
and oxidized products of various kinds
Localities.— The most important localities of cerargynte are in Peru,
Chile, Honduras and Mexico, where it is associated with native silver.
It is also found near Leadville, Colo*; near Austin, in the Comstock
lode, Nev., and at the Poorman Mine, and in other mines in Idaho
CHLORIDES, FLfORIDES, ETC
139
and at several places in Utah. Good crystals occur in the Poorman
Mine.
Extraction — When a silver ore consists essentially of cerargynte the
metal may be extracted by amalgamation Ores containing compara-
tively small quantities of cerargynte are smelted
Production — The quantity of cerargyrite mined cannot be safely
estimated. As has been stated, it is usually wrought with other silver
ores,
THE FLUORIDES
The fluorides are salts of hydrofluoric acid. There are several
known to occur as minerals, but only two, the fluoride of calcium and
FIG 60 —Group of Fluonte Crystals from Weardale, Co., Durham, England (Foote
Mineral Company )
the double fluorides of sodium and aluminium are of sufficient impor-
tance to merit description here.
Fluorite (CaF2)
Fluorite, or fluorspar, is the principal source of fluorine. It is usually
a transparent mineral that is characterized by its fine color and its hand-
140
DESCRIPTIVE MINERALOGY
some crystals (Fig 60) Perhaps there is no other mineral known that
can approach it m the beauty of its crystal groups The uncrystallized
fluorite may be massive, granular or fibrous
Fluonte is a compound of Ca and F in the proportion of 48 9 per cent
F and 51 i per cent Ca Chlorine is occasionally present in minute
quantities, and SiCfe, AkOs and Fe20s are always present A sample of
commercially prepared fluonte from Marion, Ky , gave
CaF2
94 72
Si02
I 22
CaC03
i 82
MgO
68
The crystallization is isometric (hexoctrahedral class), and inter-
penetration twins are frequent The principal forms observed are
FIG 6 1
FIG 62
FIG 61 —Crystal of Fluonte with oo O oo , 100 (a) and « 02, 210 (e).
FIG 62 — Interpeaetration Cubes of Fluonte, Twinned about O(in)
0(ui), oo O oo (100), oo 02(210) and 462(421) (Fig 61), but some crys-
tals are highly modified, as many as 58 forms having been identified upon
the species The twins, with O(ni) the twinning plane, are usually
interpenetration cubes, or cubes modified on the corners by the octa-
hedrons (Fig. 62). The mineral occurs also in granular, fibrous and
earthy masses.
The cleavage of fluorite is perfect parallel to 0(in). The mineral
is brittle, its fracture is uneven or conchoidal, its hardness is 4 and its
density about 3.2. It mdts at 1387°. Its color is some shade of yel-
low, white, red, green, blue or purple, its luster vitreous, and its streak
is white Many specimens are transparent, some are only translucent.
Most specimens phosphoresce upon heating A vanety that exhibits a
green phosphoresence is known as cfdorophane The index of refraction
for sodium light is 1 43385 at 20°. The mineral is a nonconductor of
electricity.
The color of the brightly tinted varieties was formerly thought to be
due to the presence of minute traces of organic substance since it is lost
CHLORIDES, FLUORIDES, ETC 141
or changed when the mineral is heated, but recent observations of the
effect of radium emanations upon light-colored specimens indicate a
deepening of their color by an increase in the depth of the blue tints.
This suggests that the coloring matter is combined with the CaF2- It
may be a colloidal substance
In the closed tube fluonte decrepitates and phosphoresces When
heated on charcoal it fuses, colors the flame yellowish red and yields an
enamel-like residue which reacts alkaline to litmus paper Its powder
treated with sulphuric acid yields hydrofluoric acid gas which etches
glass. The same effect is produced when the powdered mineral is fused
with four times its volume of acid potassium sulphate (HKSO*) in a
glass tube The walls of the tube near the mixture become etched as
though acted upon by a sand blast.
Fluonte is easily distinguished by its cleavage and hardness from
most other minerals It is also characterized by the possession of
fluorine for which it gives dear reactions.
Syntheses — Crystals are produced upon the cooling of a molten mix-
ture of CaF2 and the chlorides of the alkalies, and by heating amorphous
CaF2 with an alkaline carbonate and a little HC1 in a closed tube at 250°.
Occurrence, Localities and Origin. — The mineral occurs in beds, in
veins, often as the gangue of metallic ores and as crystals on the wails
of cavities in certain rocks. It is the gangue of the lead veins of northern
England and elsewhere. Handsome crystallized specimens come from
Cumberland and Derbyshire, England; Kongsberg, Norway, Cornwall,
Wales, and from the mines of Saxony. In the United States the mineral
forms veins on Long Island; in Blue Hill Bay, Maine, at Putney, in
Vermont; at Plymouth, Conn ; at Lockport and Macomb, in New
York, at Amelia Court House, Va., and abundantly in southeastern
Illinois and the neighboring portion of Kentucky, where it occurs asso-
ciated with zinc and lead ores. These last-named localities, the neigh-
borhood of Mabon Harbor, Nova Scotia, and Thunder Bay, Lake
Superior, afford excellent crystal groups. In nature fluonte has been
apparently produced both by crystallization from solutions and by
pneumatolytic processes
Since fluorite is soluble in alkaline waters, its place in the rocks is often
occupied by calcite, quartz or other minerals that pseudomorph it.
Uses — The mineral is used extensively as a flux in smelting iron and
other ores, in the manufacture of opalescent glass, and of the enamel
coating used on cooking utensils, etc It is also used in the manufacture
of hydrofluoric acid, which, in turn, is employed in etching glass The
brighter colored varieties are employed as material for vases and the
142 DESCRIPTIVE MINERALOGY
transparent, colorless kinds are ground into lenses for optical instruments
The mineral is also cut into cheap gems, l:no\vn according to color, as
false topaz, false amethyst, etc Except \\hen used for making lenses or
as a precious stone, fluorite is prepared for shipment by crushing, wash-
ing and screening A portion is ground
Production — The fluonte produced in the United States is obtained
mainly from Illinois and Kentucky, though small quantities are mined
in Colorado, New Mexico and New Hampshire The production in
1912 amounted to 116,545 tons, valued at $769,163. Of this, 114,410
tons came from Illinois and Kentucky. The imports were 26,176 tons,
valued at $71,616
THE DOUBLE CHLORIDES AND DOUBLE FLUORIDES
These double salts are apparently molecular compounds, in which
usually two chlorides or two fluorides combine, as in AlFa+3NaF
Moreover, one of the members of the combination of chlorides is nearly
always either the sodium or the potassium chloride The law of this
combination is expressed by Professor Remsen in these words " The
number of molecules of potassium or sodium chloride which combine
with another chloride is limited by the number of chlorine atoms con-
tamed m the other chloride " Thus, if NaCl makes double salts with
MC12, in which M represents any bivalent element, only two are possible,
viz- MCl2+NaCl and MCl2+2NaCl With MC13 three double salts
with sodium may be formed, etc These double salts are not regarded
as true molecular compounds, but they are looked upon as compounds
in which Cl and F are bivalent like oxygen
Carnallite (KMgCls 6H20)
Carnallite may be regarded as a hydrated double chloride of the
composition MgCk KC1 6H2O with 14 i per cent K, 8 7 per cent Mg,
38 3 per cent Cl and 39 o per cent H20 It occurs m distinct crys-
tals but more frequently in massive granular aggregates
Its crystallization is orthorhombic (bipyramidal class), but the habit
of its crystals is usually hexagonal because of the nearly equal develop-
ment of pyramids and brachydomes. Its axial ratio is .5891 i i 3759.
Crystals are commonly bounded by oo P(no), P(in), JP(ri2), £P(ii3),
oo P eo (oio), 2? a& (021), P 56 (on), |P oa (023), oP(ooi), and P 56 (101).
The angle no A 3 10=61° 2oJ'.
Carnallite is colorless to milky white, transparent or translucent,
and has a fatty luster Many varieties appear red in the hand specimens
CHLORIDES, FLUORIDES, ETC 143
because of the inclusion of numerous small plates of hematite or goethite,
or yellow because of inclusions of yelkm liquids or tiny crystals. The
mineral has a hardness of 1-3, and a density of 1.60 It possesses no
cleavage but has a conchoidal fracture It is not an electrical conductor.
It is deliquescent and has a bitter taste Its indices of refraction for
sodium light are a= i 467, jS= 1.475, 7= 1-494
Before the blowpipe carnalhte fuses easily. In the closed tube it
becomes turbid and gives off much water, which is frequently accom-
panied by the odor of chlorine. It melts in its own water of crystalliza-
tion. When evaporated to dryness and heated by the blowpipe flame
a white mass results which is strongly alkaline. The mineral dissolves
in water, forming a solution which reacts for Mg, K and Cl
Carnalhte is easily recognized by its solubility, its bitter taste and the
reaction for chlorine
Synthesis — The mineral separates in measurable crystals from a solu-
tion of MgCl2 and KC1
Occurrence and Origin — Carnalhte occurs hi beds associated with
sylvite, halite, kieserite (p. 246), and other salts that have been pre-
cipitated by the evaporation of sea water or the water of salt lakes
Localities — It is found in large quantity at Stassfurt, Germany, at
Kalusz, in Galicia and near Maman, in Persia
Uses. — Carnalhte is used as a fertilizer and as a source of potash
salts.
Cryolite (NasAlFe)
Cryolite usually occurs as a fine-grained granular white mass in
which are often embedded crystals of light brown iron carbonate (sider-
ite). The formula given above demands 54 4 per cent F, 12 8 per cent
Al and 32.8 per cent Na. Analyses of pure white specimens correspond
veiy closely to this
The mineral is monoclinic (prismatic class), but crystals are exceed-
ingly rare and when found they have a cubical habit. Their axial ratio
is a : b : ^=.9662 : i . i 3882. £=89° 49'. The principal forms are
ooP(no), oP(ooi), Pco(oTo), —P 00(010) and P 06(100), thus re-
sembling the combination of the cube and octahedron. Twins are com-
mon, with oo P(no) the twinning plane
The deavage of cryolite is perfect parallel to oP(coi). Its fractine
is uneven. Hardness is 2 5 and density about 3. Its color is snow-white
inclining to red and brown. Its luster is vitreous or greasy and the
mineral is translucent to transparent Because of its low index of
refraction, massive specimens suggest masses of wet snow. The re-
144 DESCRIPTIVE MINERALOGY
fractive index /3 for sodium light is i 364 It is a nonconductor of
electricity.
Cryolite is very easily fusible, small pieces melting even at the low
temperature of a candle flame The mineral is soluble in sulphuric acid
with the evolution of HF When fused in the closed tube with KHS04
it yields hydrofluoric acid, and -ft hen fused on charcoal fluorine is evolved
The residue treated with Co(NOs)2 and heated gives the color reaction
forAl
By the aid of its reactions with sulphuric acid, its fusibility and its
physical properties cryolite is easily distinguished from fluonte, which it
most resembles, and from all other minerals.
Occurrence, Localities and Origin —The occurrences of cryolite are
very few It has been found in small quantities near Miask in the
Ihnen Mts, Russia, near Pike's Peak, Colo, and in the Yellowstone
National Park. Its puncipal occurrence is m a great pegmatitic vein
cutting granite near Ivigtut, Greenland, whence all the mineral used
in the arts is obtained The associates of the cryolite at this place are
sidente, galena, chalcopynte, p^nte, fluonte, topaz and a few rare
minerals The vein is said to be intrusive into the granite. It is
believed to be a magmatic concentration
Uses. — Cryolite was formerly employed principally in the manufac-
ture of alum and of salts of sodium. At present it is used as a flux in
the electrolytic production of aluminium, and is employed in the man-
ufacture of white porcelain-like glass, and in the process of enameling
iron The mineral is quarried in Greenland and imported into the
United States to the extent of about 2,500 tons annually. Its value is
about $25 per ton.
THE OXYCHLORIDES
The oxychlorides are combinations of hydroxides and chlorides
Some of them are " double salts " in the sense in which this word is
explained above. Atacamite is a combination of the oxychlonde
Cu(OH)Cl with the hydroxide Cu(OH)2, or Ncu Cu(OH)2.
Atacamite (Cu(OH)Cl-Cu(OH)2)
Atacamite is especially abundant in South America The mineral
is usually found in crystalline, fibrous or granular aggregates of a bright
green color
Analyses of specimens from Australia and from Atacama, Chile, yield.
CHLOEIDES, FLUORIDES, ETC 145
Cl
Cu
CuO
H20
Total
16 44
14 67
5664
12 O2
99 77
IS 83
14 16
55 7°
14 31
IOO 00
Austraha
Atacama, Chile.
The formula lequires 16 6 per cent Cl, 14.9 per cent Cu, 55 8 per cent
CuO and 12 7 per cent EkO.
The crystallization of atacamite is orthorhombic (bipyramidal class),
with a : b : £=.6613 : i : .7529 Its crystals are usually slender prisms
bounded by ooP(no), ooP£(i2o), ooPoo (oio), P66 (011), oP(ooi)
and P(III), or tabular forms flattened m the plane of the macropinacoid
oo P 56 (100). Twins are common, with the twinning plane ooP(no).
The cleavage of atacamite is perfect parallel to oo P 06 (oio). Its
fracture is conchoidal. Its hardness is 3-3 5 and density about 3 76.
Pure atacamite is of some shade of green, varying between bright shades
and emerald. Its aggregates often contain red or brown streaks or
grains due to the admixture of copper oxides. It is transparent to trans-
lucent. The streak of the mineral is apple-green It is a nonconductor
of electricity Its indices of refraction for green light are a=i 831,
0= 1.861,7=1 880
In the closed tube atacamite gives off much water with an acid reac-
tion, and yields a gray sublimate In the oxidizing flame it fuses and
tinges the flame azure blue (reaction for copper chloride). It is easily
reduced to a globule of copper on charcoal and is easily soluble in acids.
Atacamite is readily distinguished from garmerite, malachite and
other green minerals by its solubility in acids without effervescence and
by the azure blue color it imparts to the flame.
Synthes^s. — Crystals have been produced by heating cuprous oxide
(CugO) with a solution of FeCls, in a closed tube at 250°.
Occurrence, Localities and Origin — The mineral is most abundant
along the west side of the Andes Mountains in Chile and Bolivia. It
occurs also in South Australia, in India, at Ambriz, on the west coast of
Afnca, in southern Spain, in Cornwall, where it forms stalactite tubes,
in southern California, and near Jerome, Arizona. It is formed as the
result of the alteration of other copper compounds, and is found most
abundantly in the upper portions of copper veins Atacamite changes
on exposure to the weather into the carbonate, malachite, and the sili-
cate, chrysocolla.
Uses. — The mineral is an important ore of copper, but it is mined
with other compounds and consequently no records of the quantity
obtained are available.
CHAPTER VII
THE OXIDES
THE oxides (except water) and the hydroxides may be regarded as
derivatives of water, the hydrogen being replaced wholly or in part
by a metal. When only part of the hydrogen is replaced an hydroxide
results, when all of the hydrogen is replaced an oxide results Thus,
sodium hydroxide, NaHO, may be looked upon as HgO, in which Na has
replaced one atom of H, and sodium oxide, Na20, as KfeO in which both
hydrogen atoms have been replaced by this element Ferric oxide and
ferric hydroxide bear these relations to water:
H-0— H
H— O— H, Fe— O— Fe, feme oxide, H— O— Fe, ferric hydroxide
YFe203 H-0/ Fe(OH)3
The oxides constitute a very important, though not a large, class of
minerals Some of them are among the most abundant of all minerals
They are separated into the following groups: Monoxides, sesqui-
oxides, dioxides and higher oxides.
THE MONOXIDES
Ice (H2O)
The properties of ice are so well known that they need no special
description in this place The mineral is never pure, since it contains,
in all cases, admixtures of various soluble salts. Its crystallization is
hexagonal and probably trigonal and hemimorphic (ditngonal pyram-
idal class). Crystals are often prismatic, as when ice forms the cover-
ing of water surfaces, or the bodies known as hailstones In the form
of snow the crystals are often stellate, or skeleton crystals, and sometimes
146
OXIDES
147
hollow prisms The principal forms observed on ice crystals are oP(oooi)
ooP(ioTo), |P(iol2), P(ioTi) andtfUoli) (Fig 63).
The hardness of ice is about 1.5 and its density 9181 It is trans-
parent and colorless except m large masses when it appears bluish. Its
fracture is conchoidal It possesses no distinct cleavage Its fusing
FlG. 63 — Photographs of Snow Crystals, .Magnified about 15 Diameters (After
Benttey and Perkins )
point is o° and boiling point 100°. It is a poor conductor of electricity.
Its indices of refraction for sodium light at 8° are: «= 1.3090, €= 1.3133.
COPPER OXIDES
There are two oxides of copper, the red cuprous oxide (Cu2O) and
the black cupric oxide (CuO). Both are used as ores, the former being
much more important a source of the metal than the latter
Cuprite (Cu2O)
Cuprite occurs in crystals, in granular and earthy aggregates and
massive The mineral is usually reddish brown or red and thus is easily
distinguished from most other minerals. Its composition when pure is
88.8 per cent Cu and n 2 per cent O.
In crystallization the mineral is isometric, in the gyroidal hemihedral
division of the system (pentagonal icositetrahedral dass). Its pre-
148 DESCRIPTIVE MINERALOGY
dominant forms axe ooOoo(ioo), 0(iu), ooO(uo), 0002(210),
202(211), 20(221) and 301(321), sometimes lengthened out into
capillary crystals, producing fibrous varieties (var chdcotr^ch^te).
The cleavage of cupnte is fairly distinct parallel to O(in) Its frac-
ture is uneven or conchoidal Its hardness is 3 5-4 and density about 6
The mineral is in some cases opaque, oftener it is translucent or even
transparent in very thin pieces By reflected light its color is red,
brown and occasionally black. By transmitted light it is crimson When
gently heated transparent varieties turn dark and become opaque, but
they reassume their original appearance upon cooling. Its streak is
brownish red and has a brilliant luster When rubbed it becomes yellow
and finally green. The luster of the mineral vanes between earthy and
almost vitreous It is a poor conductor of electricity, but its con-
ductivity increases rapidly with using temperature. Its refractive index
for yellow light = 2.705
In the blowpipe flame cuprite fuses and colors the mantle of the
flame green If moistened with hydrochloric acid before heating the
flame becomes a brilliant azure blue. On charcoal the mineral first
fuses and then is reduced to a globule of metallic copper. It dissolves in
strong hydrochloric acid, forming a solution which, when cooled and
diluted with cold water, yields a white precipitate of cuprous chloride
(Cu2Cl2).
Cupnte may easily be distinguished from other minerals possessing
a red streak by the reaction for copper — such as the production of a
metal globule on charcoal, and the formation of cuprous chloride in con-
centrated hydrochloric acid solutions by the addition of water. More-
over, the mineral is softer than hematite and harder than reaglar, cin-
nabar and proitsttte.
Cuprite suffers alteration very readily. It may be reduced to native
copper, in which case the copper pseudomorpbs the cuprite, or, on ex-
posure to the air it may be changed into the carbonate, malachite,
pseudomorphs of which after cupnte are common.
Syntheses — Crystals of cupnte have frequently been observed on
copper utensils and coins that had been buried for long periods of time.
Crystals have also been obtained by long-continued action of NHs upon
a mixture of solutions of the sulphates of iron and copper, and by heating
a solution of copper sulphate and ammonia with iron wire in a dosed tube
Occurrence^ Origin and Localities — Cuprite often occurs as well
defined crystals embedded in certain sedimentary rocks in the upper,
oxidized portions of copper veins, and in masses m the midst of other
copper ores, from which it was produced by oxidation processes* It is
OXIDES 149
found as crystals in Thuringia, in Tuscany, on the island of Elba, in
Cornwall, Eng , at Chessy, France, and near Coquimbo, in Chile.
In Chile, m Peru, and in Bolivia it exists in great masses
In the United States it occurs at Cornwall, Lebanon Co , Penn. It
is also found associated with the native copper on Keweenaw Point,
Mich , at the copper mines in St. Genevieve Co , Mo ; at Bisbee and
at other places in Arizona The fibrous vanety known as chalcoinchite
is beautifully developed at Morenci in the same State.
Uses —Cuprite is mined with other copper compounds as an ore of
copper.
Melaconite, or Tenorite (CuO)
Melaconite, or tenonte, is less common than cuprite. It usually
occurs in massive forms or in earthy masses Crystals are rare Its
composition is 79 8 per cent Cu and 20 2 per cent 0.
In crystallization melacomte is tnchnic with a monochnic habit.
Its axial ratio is a : b : c=i 4902 : i : 1 3604 and £=99° 32'. The
angles a and 7 are both 90°, but the optical properties of the crystals
proclaim their tnchnic symmetry.
The mineral possesses an easy cleavage parallel to oP(ooi). Its frac-
ture is conchoidal and uneven, its hardness 3 to 4 and density about 6.
When it occurs in thin scales its color is yellowish brown or iron gray.
When massive or pulverulent it is dull black. Its streak is black, chang-
ing to green when rubbed. Its refractive index for red light is 2 63.
It is a nonconductor of electricity.
The chemical reactions of melaconite are precisely like those of cu-
pnte, with the exception that the mineral is infusible.
Melaconite is distinguished from the black minerals that contain no
copper by its reaction for this metal It is distinguished from covelhte
and other dark-colored sulphides containing copper by its failure to give
the sulphur reaction.
Syntheses — Crystals of melaconite have been found in the flues of
furnaces in which copper compounds and moist NaCl are being treated.
They have also been obtained by the decomposition of CuCk by water
vapor
Occurrence, Localities and Origin.— The mineral usually occurs associ-
ated with other ores of copper, from which it has been formed, in part
at least, by decomposition. It is mined with these as jmt ore. Thin
scales are found on the lava of Vesuvius, where it must have been f onned
by sublimation. Masses occur at the copper mines of Ducktowu, Temi.
150 DESCRIPTIVE MINERALOGY
Zincite (ZnO)
Zincite is the only oxide of the zinc group of elements known It is
rarely found in crystals It usually occurs m massive forms associated
with other zinc compounds.
Pure zmcite is a compound containing 80 3 per cent Zn and 19 7 per
cent 0, Since, however, the mineral is frequently admixed with man-
ganese compounds it often contains also some manganese and a little
iron. A specimen from Sterling Hill, N J ,
gave 98 28 per cent ZnO, 6 50 per cent MnO
and 44 per cent Fe20g
Natural crystals of zmcite are very rare
From a study of artificial crystals it is known
that the mineral is hexagonal and hemimorphic
(dihexagonal pyramidal class). The principal
forms observed are ooP(ioTo), ooP2(ii2o),
oP(oooi), P(ioTi), P2(ii22) and various other
Fro. 64 —Zincite Crystal pyramids of the ist and 2d orders Their habit
with oop, iolo (m). 1S hemimorphic with P(iori) and oP(oooi) at
p, roll (p) and oP, ^ oppOSite ends of a short columnar crystal
0001 W (Fig. 64)
The cleavage of ^incite is perfect parallel to oP(oooi) Its fracture
is conchoidal, its hardness 4-4 5 and density about 5 8 Although color-
less varieties are known, the mineral is nearly always deep red or orange-
yellow, due most probably to the manganese present in it The streak
of the red varieties is orange- yellow. Its indices of refraction are
about 2 The mineral is a conductor of electricity.
When heated in the closed tube the common variety of zmcite
blackens, but it resumes its original color on cooling With the borax
bead it gives the manganese reaction Heated on charcoal it coats the
coal with a white film, which, when moistened with cobalt solution and
heated again with the oxidizing flame of the blowpipe, turns green The
mineral dissolves in acids
When exposed to the atmosphere zmcite undergoes slow decomposi-
tion to zinc carbonate
Syntheses — Zinc oxide crystals are frequent products of the roasting
of zinc ores in ovens They have also been produced by the action of
zinc chloride vapor upon lime and by the action of water upon zinc
chloride at a red heat.
Occurrence and Locafofoes — The mineral occurs only in a few places
It is found with other zinc and manganese minerals near Ogdensburg,
OXIDES 151
and at Franklin Furnace, m Sussex Co , N J , m the form of great
layers in marble, that are bent into troughs The lajers are probably
veins that were filled from below by emanations from a great underground
reservoir of igneous rock
Uses — Most of the zmcite produced in the United States is used in
the manufacture of zinc oxide The ore, which consists of a mixture of
zincite, franklimte (see p 199), and willemite (see p 306), is crushed
and separated into its component parts by mechanical processes The
separated zmcite is then mixed with coal and roasted The zinc oxide
is volatilized and is caught m tubes composed of bagging. The willemite
and franklimte are smelted to metallic zinc and the residues are used m
the manufacture of spiegeleisen
Production — Formerly this mineral, together TMth the silicate found
associated with it in New Jersey, constituted the most important source
of zinc in this country At present most of the metal is obtained from
sphalerite Of the 380,000 tons of zinc in spelter and zinc compounds
produced in the United States during 1912 about 69,760 tons were
made from zmcite and the ores associated with it. This had an esti-
mated value of $9,626,991.
THE SESQUIOXIDES
The sesquioxides (R20s) include a few compounds of the nonmetals
that are comparatively rare and a group of metallic compounds that
includes two minerals of great economic importance. One of these,
hematite (FeaOa), is the most valuable of the iron ores
ARSENOLITE— CLAUDETITE GROUP
The only group of the nonmetallic sesquioxides that need be referred
to in this place comprises those of arsenic and antimony. This is an
isodimoiphous group including four minerals.
Isometric Monochmc
Arsenohte As20s Claudetite
Senarmoutote Sb20s Valenttmte
All the minerals of the group are comparatively rare. The isometric
forms occur in well developed octahedrons and in crusts covering other
minerals They are also found in earthy masses. It is probable that at
high temperatures the isometric forms pass over into the monodinic
modifications, as some of the latter have been abserved to consist of
aggregates of tiny octahedrons. Crystals of daudetite are distinctly
152 DESCRIPTIVE MINERALOGY
monoclinic, but they are so thinned as to possess an orthorhombic
habit Valentmite crystals, on the contrary, appear to be plainly
orthorhombic, but their apparent orthorhombic symmetry may be
due to submicroscopic twinning of the same character as that in
claudetite, but which in the latter mineral is macroscopic
All four minerals occur as weathered products of compounds contain-
ing As or Sb They give the usual blowpipe reactions for As or Sb
In the closed tube they melt and sublime
Arsenolite (As2Os) is colorless or white Its specific gravity is 3,7
and refractive index for sodium light = i 755 It usually occurs in octa-
hedrons, or m combinations of 0(in) and ooO(no), but these when
viewed in polarized light are often seen to be amsotropic The mineral is
found also in aggregates of hair-like crystals with a hardness of i 2 It is
soluble in hot water, yielding a solution with a sweetish taste
Senarmonite (SbgOs) is gray or white Its density is 5 2 and
n=2 087 for yellow light Its octahedral crystals are also often aniso-
tropic, its hardness=2 It is soluble in hot HC1 but is only very
slightly soluble in water When heated it turns yellow, but becomes
white again upon cooling
Claudetite (As2Os) is monochmc prismatic, with a : b : c= 4040 : i
: 3445 and /3=86° 03' Its white crystals are usually tabular parallel
to oo P ao (oio) and are twinned, with oo P 56 (100) the twinning plane
Their cleavage is parallel to oo P o> (oio) and their density is 4 15
H= 2.5 The mineral is an electrical nonconductor
Valentinite (Sb2Os) is apparently orthorhombic bipyramidal (pos-
sibly monoclimc prismatic) with a : b : c= 3914 • i 3367 Its crystals
are tabular or columnar in habit and are very complex The mineral is
found also in radial groups of acicular crystals and m granular and
dense masses Its color is white, pink, gray or brown, and streak
white Its density is 5 77 and hardness 2 5-3. It is insoluble in HC1
It is a nonconductor of electricity
CORUNDUM GROUP
t
The sesquioxides of aluminium and iron constitute an isomorphous
group crystallizing in the rhombohedral division of the hexagonal sys-
tem (ditngonal scalenohedral class) Both the aluminium and iron
compounds, corundum and hematite^ are of great economic importance
OXIDES
153
Hematite (Fe20a)
Hematite is one of the most important minerals, if not the most
important one, from the economic standpoint, smce it is the most val-
uable of all the iron ores It is known by its dark color and its red
powder It occurs in black, glistening crystals, in yellow, brown or red
earthy masses, in granular and micaceous aggregates and in botiyoidal
and stalactitic forms
Chemically, the mineral is Fe20a corresponding to 30 per cent 0 and
70 per cent Fe. In addition to these constituents, hematite often con-
tains some magnesium and some titanium. By increase in the latter
element it passes into a mineral which has not been distinguished from
ilmenite (see p 462)
The habit of hematite crystals is nearly always rhombohedraL
FIG* 65— Hematite Crystals with R, loTi (r), |P2, 2243 (*), JR 1014 («), oop2l
1 1 20 (0) and oR, oooi (c)
Their axial ratio is a : c=i : 1.3658, and the predominant forms are
R(ioTi), iR(iol4), ^2(2243), the prisms oo P(ioTo) and ooP2(ii2o)
and often the basal plane (Fig. 65) In addition, about no other forms
have been identified The crystals are often tabular, and sometimes
are grouped into aggregates resembling rosettes. In many cases the
terminal faces are rounded A parting is often observed parallel to
the basal plane, due to the occunence of the mineral in aggregates in
which each crystal is tabular.
Hematite has no well defined cleavage Its fracture is conchoidd or
earthy. Its crystals are black, glistening and opaque, except in very
small splinters These are red and transparent or translucent. Earthy
varieties are red. The streak of all varieties is brownish red or cherry-
red. The hardness of the crystallised hematite is 5.5-6.5 aad its density
about 5.2. It is a good conductor of electricity. Its refractive indices
are: 60=3.22, 6=2.94 for yellow light.
The mineral is infusible before the blowpipe. In the reducing flame
on charcoal it becomes magnetic, and when heated with soda it is reduced
to a magnetic metallic powder It is soluble IB strong hydrochloric acid.
154 DESCRIPTIVE MINERALOGY
The crystalline and earthy aggregates of hematite to which distinct
names have been given are
Specular, when the aggregate consists of grains with a glistening,
metallic luster, like the luster of the crystals When the grains are thin
tabular the aggregate is said to be micaceous
Columnar or fibrous, when in fibrous masses The color is usually
brownish red and the luster dull The botryoidal, stalactic and various
imitative forms belong here Red hematite is a compact red variety in
which the fibrous structure is not very pronounced
Red ocher is a red earthy hematite mixed with more or less clay and
other impurities
Clay ironstone is a hard brownish or reddish variety with a dull luster
It is usually a mixture of hematite with sand or clay
Oolitic ore is a red variety composed of compacted spherical or nearly
spherical grams that have a concentric structure
Fossil ore differs from oolitic ere mainly in the fact that there are
present in it small shells and fragments of shells that are now composed
entirely of hematite
Martite is a pseudomorph of hematite after magnetite.
Hematite is distinguished from all other minerals by its red powder
and its magnetism after roasting
Syntheses — Crystals of hematite are obtained by the action of steam
on ferric chloride at red heat, by heating ferric hydroxide with water
containing a trace of NH*F to 250° in a closed tube, and by cooling a
solution of Fe20s in molten borax or halite
Occurrence and Origin — Hematite is found in beds with rocks of
nearly all ages It occurs also as a deposit on the bottoms of marshy
ponds, and m small grams m the rocks around volcanic vents The
crystallized variety is often deposited on the sides of clefts in rocks near
volcanoes and on the sides of certain veins It is produced by sublima-
tion, by sedimentation and by metasomatic processes
Localities —Handsome crystals occur on the island of Elba, near
Limoges in France, m and on the lavas of Vesuvius and Etna, at many
places in Switzerland, Sweden, etc , and at many in the United States
Beds of great economic importance occur m the Gogebic, Menommee
and Marquette districts in Michigan; m the Mesabe and Vermilion
districts in Minnesota, m the Pilot Knob and Iron Mountain districts
in Missouri, and in the southern Appalachians, especially m Alabama
Uses. — In addition to its use as an ore the fibrous variety of hematite
is sometimes cut into balls and cubes to be worn as jewelry. The earthy
varieties are ground and employed in the manufacture of a dark red
OXIDES 155
paint such as is used on freight cars, and the ponder of some of the mass-
ive forms is used as a polishing ponder
Prodtiction.—Most of the iron ore produced in the United States is
hematite, and by far the greater proportion of it comes from the Lake
Superior region The statistics for 191 2 follow
QUANTITY (IN LONG TONS) OF IRON ORE MINED IN THE SEVERAL LEAD-
ING STATES DURING 1912
Hematite Other Iron Ores Total
Minnesota ..... 34j43i,o°o . . 34,431,000
Michigan ..... 11,191,000 11,191,000
Alabama . . . 3,814,000 749,ooo 4,563,000
New York . 106,327 1,110,000 1,216,327
Wisconsin 860,000 860,000
Tennessee. 246,000 171,000 417,000
Total in U S . 51,345,782 3,804,365 55,150,147
The total production in 1912 was valued at about $104,000,000
Corundum
Corundum is the hardest mineral known, with the exception of dia-
mond In consequence of its great hardness an impure variety is used
as an abrading agent under the name of emery. It is also one of the
most valuable of the gem minerals It occurs as crystals and in granular
masses
The mineral is nearly always a practically pure oxide of aluminium of
the composition AkOs, in which there are 52 9 per cent Al and 47 i per
cent O The impure varieties usually contain some iron, mainly as an
admixture in the form of magnetite
The axial ratio of corundum crystals is i : i 36 The forms are
usually simple pyramids, among which |P2(2243) and |P2(44S3)
are the most common (Fig. 66), and the prism oo P2(ii2o) The basal
plane is also common (Fig 67). Many crystals consist of a series of
steep prisms and the basal plane, with a habit that may be described as
barrel-shaped (Fig 68) The crystals are often rough with rounded
edges The prismatic and pyramidal faces are usually striated hori-
zontally, and the basal plane by lines radiating from the center
All corundum crystals are characterized by a parting parallel to the
basal plane, and often by a cleavage parallel to the rhoinbohedron, due
to the presence of lamellae twinned parallel to R(ioli). The fracture
o£ the mineral is conchoidal or uneven. Its density is about 4 and its
156
DESCRIPTIVE MINERALOGY
hardness 9 The mineral possesses a vitreous to adamantine luster It
is transparent or translucent Its streak is uncolored Its color varies
from white, through gray to vanous shades of red, yellow, or blue
The blue varieties are pleochroic in blue and greenish blue shades The
mineral is a nonconductor of electricity. Its refractive indices for
yellow light are w=i 7690, €=i 7598.
Three varieties of corundum are recognized in the arts: Sapphire,
corundum and emery
Sapphire is the generic name for the finely colored, transparent or
translucent varieties that are used as gems, watch jewels, meter bearings,
etc. The sapphires are divided by the jewelers into sapphires, possessing
FIG 66
FIG 67
FIG 68
FIG 66 — Corundum Crystal with |P2, 4483 (u)
Fee. 67— Corundum Crystal with R, loYi (r), °oPs, 1120 (a), and oR, oooi (c)
FIG. 68 — Corundum Crystal Form a, v and c as in previous figures Also £P2,
2243 (n) and — 2R, 0221 ($)
a blue color, rubies, possessing a red shade, Oriental topazes, Oriental
emeralds and Oriental amethysts having respectively yellow, green and
purple tints.
Corundum is the name given to dull colored varieties that are ground
and used as polishing and cutting materials
Emery is an impure granular corundum, or a mixture of corundum
with magnetite (FeaO^) and other dark colored minerals Emery, like
corundum, is used as an abrasive. It is less valuable than corundum
powder because it contains a large proportion of comparatively soft
material
Powdered corundum when heated for a long time with a few drops of
cobalt nitrate solution assumes a blue color The mineral gives no
definite reaction with the beads It is infusible and insoluble. It is
OXIDES 157
most easily recognized by its hardness The mineral alters to spinel
(p 196) and to fibrous and platy aluminous silicates
Syntheses —Corundum crystals have been produced artificially in
many different ways, but only recently has the manufacture of the gem
variety been accomplished on a commercial scale Amorphous Al2Cs
dissolves in melted sodium sulphide and crystallizes from the glowing
mass at a red heat By melting Al20s in a mass of some fluoride and.
potassium carbonate containing a little chromium, and using~compara-
tively large quantities of material, violet and blue rubies were obtained
by Fremy and Verneuil Rubies are also produced by melting AfaOs
and a little C^Os for several minutes at a temperature of 2250° C in
an electric oven
In recent years reconstructed rubies have become a recognized article
of commerce These are crystalline drops of ruby material made by
melting tiny splinters and crystals of the mineral in an electric arc
Alundum is an artificial corundum made by subjecting the aluminium
hydroxide, bauxite, to an intense heat (5ooo°-6ooo°) m an electric
furnace.
Occurrence and Origin — Corundum usually occupies veins in crys-
talline rocks or is embedded in basic intrusive rocks and in granular
limestone The sapphire varieties are also often found as partially
rounded crystals in the sands of brook beds The varieties found in
igneous rocks are primary crystallizations from the magmas producing
the rocks. The varieties in limestones are the result of metamorphic
processes
Localities — Sapphires are obtained mainly from the limestone of
Upper Burma They are known also to occur in Afghanistan, in Kash-
mir and in Ceylon They are occasionally found in the diamond-bearing
gravels of New South Wales and in the bed of the Missouri River, near
Helena, Montana In the United States sapphire is mined near the
Judith River in Fergus Co , and in Rock Creek in Granite Co., Mont.,
where it occurs in a dike of the dark igneous rock known as monduquite,
and is washed from the placers of three streams in the same State. The
only southern mines that have produced gem material are at Franklin
and Culsagee, N. C , and from these not any great quantity of stones of
gem quality have been taken
The largest sapphire crystal ever found was taken, however, from
one of them It weighs 312 Ib , is blue, but opaque. From one of
these mines, also, came the finest specimen cf green sapphire (Oriental
emerald) ever found
Corundum in commercial quantities occurs on the coast of Malabar,
158 DESCRIPTIVE MINERALOGY
m Siam, near Canton, China, and in southeastern Ontario, Canada.
Emery is obtained from several of the Grecian Islands, more particularly
Naxos, and from Asia Minor It is mined in the United States at Chester,
Mass, and at Peekskill, N Y Crystallized corundum occurs near
Litdxfield, Conn , at Greenwood, Maine, at Warwick and Amity, N Y ,
at Mineral Hill, Penn , m Patrick Co , Va , at Corundum Hill and at
Laurel Creek, Macon Co., N C , and at \ anous points in Georgia, at
all of which places it has been mined In all the localities within the
United States the corundum occurs on the peripheries of masses of
pendotite (ohvine rocks)
Uses — Corundum, emery and alundum, after crushing and washing,
are used as abrasives and m the manufacture of cutting wheels.
Production. — The amount of sapphire produced in the United States
m 1912 was valued at $195,505 Most of it was used for mechanical
purposes, but 384,000 carats were used as gem material
Most of the corundum used in the United States is imported from
Canada, where it occurs in Hakburton, Renfrew and neighboring coun-
ties in Ontario, as crystals scattered through the coarse-grained crys-
talline rocks known as syenite, nephelme syenite and anorthosite
Most of the emery is also imported Only 992 tons with a value
of $6,652 were mined in 1912 The imports of corundum and emery
were valued at $501,725, but the importation of these substances is
gradually diminishing because of the rapid increase in the amounts
of alundum and carborundum manufactured In 1912 the production
of alundum reached 13,300,000 Ib valued at $796,000,
THE DIOXIDES
THE KONMETALLIC DIOXIDES
There are but few dioxides of the nonmetals that occur as minerals,
and only one of these, quartz, is abundant
SILICA GROUP
Silica (SiOa) occurs in nature in four or five important modifica-
tions as follows.
a Qmrtz, tngonal-trapezohedral class, below 575°.
j8 Quartz, hexagonal-trapezohedral class, above 575° and below 870°
Tridymite, rhombic bipyramidal, pseudohexagonal habit. Hex-
agonal above 117°.
Cristobdite, tetragonal system, pseudocubic habit Isometric above
140°.
OXIDES
159
Chalcedony is regarded by many mineralogists as a form of quartz,
but its index of refraction for red light is n=i 537, which is noticeably
lower than that of either ray in quartz, which is ««i 5390, e=i 5480
for the same color Its hardness also is a little less than that of quartz.
Some mineralogists believe that all of these properties may be explained
on the assumption that the mineral is a mass of fine quartz fibers, perhaps
mixed with other substances, but those \vho have investigated it by
high temperature methods are inclined to regard it as a distinct mineral
Quartz (Si02)
Quartz vies with calcite for the commanding position among the
minerals It is very abundant, and appears under a great variety of
FIG 69
FIG 70.
FEG 69 — Quartz Crystal Exhibiting Rhombohedral Symmetry R, loir (r), — R,
oili (s) and °° R, loTb (m)
FIG 70 — Ideal (A) and Distorted (B) Quartz Crystals Bounded by same Forms as
m Fig 69
forms Often it occurs in distinct crystals At other times it appears
as grains without distinct crystal forms, and again it constitutes great
massive deposits
Pure quartz consists of 46 7 per cent Si and 53.3 per cent (X Mass-
ive varieties often contain, in addition, some opal (Si(OH)4), and traces
of iron, calcite (CaCOs), clay, and other impurities
The crystallization of quartz is in the trapezohedral tetartohedral
division of the hexagonal system (trigonaUrapezohedral class), at tem-
peratures below 575°. When formed above this temperature its sym-
metry is hexagonal trapezohedral (hemihedral). The former is known as
a. quartz, and the latter as jS quartz. They readily pass one into the
other at the stated temperature. The axial ratio is i : i.i. The prin-
_ _ — 2P2 —
cipal forms observed are +R(ioii), -R(om), oo R(ioio), — (1121),
160
DESCRIPTIVE MINERALOGY
(Fig 74) and a series of steep rhombohedrons and trapezo-
hedrons Although these may all be tetartohedral since t he geometrical
FIG 71 — Etch Figures on Two Quartz Crystals of the Same Form, Illustrating Dif-
ferences in Symmetry \ Right-Hand Crystal B Left-Hand Crystal
(After Penfidd )
FIG 72 — Group of Quartz Crystals with Distorted Rhombohedral Faces (Foote
Mineral Company )
forms of the first four are not distinguishable from the corresponding
hemihedral ones, the crystals possess a rhombohedral symmetry (Fig.
69). The angle ioTiA"iioi = 850 46'
OXIDES
161
Often the +R and the -R faces are equslly de\ eloped so that they
appear to belong to the hexagonal pyramid P (Fig yoA) Their true
character, ho\\ever, is clearly brought out by etching, when figures are
produced on the +R and the -R that are differently situated with
respect to the edges of the faces (Fig 71) On the other hand, on many
crystals some of the R faces are very much enlarged at the expense of
the others (Fig 72)
The crystals are commonly pnsmatic Often they are so dis-
FIG 73 FIG 74
FIG 73 — Tapenng Quartz Crystal with Rhombohedral Symmetry \ Combination
of r, z, m and Two Steep Rhombohedrons B Cross-section near Top.
FIG 74 — Quartz Crystals Containing ooR, iolo (m), R, loll (r), — R, oiTi (s),
), — r, 510*1 (*)
and — /, sin
2
onB
), — -/, sT6"i (*) on A, and — r, 1121
2 2
torted that it is difficult to detect the position of the c axis (Fig
708) The stnations on oo R(ioTb) are, however, always parallel to
the edges between R and ooR When these are sharply marked the
position of the vertical axis is easily recognized Many crystals
taper sharply toward the ends of the c axis This tapering is due to
oscillatory combination of the prism ooR with rhombohedrons
(Fig- 73)-
The habits of the crystals vary with the crystallization of the quartz.
On crystals of the 0 phase the +R and — R faces are equally developed
and trigonal trapezohedrons are absent. The crystals are hexagonal in
162
DESCRIPTIVE MINERALOGY
habit Crystals of the a phase usually exhibit marked differences in
the size and character of the rhombohedral planes, and trigonal trape-
zohedrons may be present on them Such crystals are usually trigonal
in habit and prismatic
The small —(1121) faces on all types of crystals (Fig 74) are
2
always striated parallel to the edge between this plane and +R. By
their aid the +R can always be distinguished from the — R This is a
matter of some practical importance since plates cut from quartz crystals
possess the power of rotating a ray of polarized light. The plates cut
C D
FIG 75 —Supplementary Twins of Quartz
C is a combination of A and B in Fig 74 twinned about *> P2(ii2o) This is
known as the Brazil law
D is a combination of two crystals like B twinned about c as the twinning axis
One is revolved 60° with reference to the others, thus causing the r and s faces to
fall together Swiss law E is a twin like D, showing portions of planes belonging
to each individual It contains also the form s.
from some crystals turn the ray to the right; those cut from others turn
it to the left Crystals that produce plates of the first kind are known
as right-handed crystals, those that produce plates of the second kind as
left-handed crystals. Since this property of quartz plates is employed
in the construction of optical instruments for use m the detection of
sugars and certain other substances in solution it is important to be
able to distinguish those crystals that will yield right-handed plates from
those that will yield left-handed ones Observation has shown that
_
when the - (1121) faces are in the upper right-hand corner of the oo R
plane immediately beneath +R the crystal is right-handed When
these faces are in the upper left-hand corner of this oo R plane the crystal
OXIDES 163
is left-handed In either case, when (5i5i) is present it occurs
4
2p2
between -- (1121) and the oo R face beneath +R
Interpenetration t\\ms of quartz are so common that few crystals
can be observed that do not exhibit some evidence of thinning (Fig 75).
The twinning plane is oo R, so that the c axes in the twinned individuals
are parallel and, indeed, often coincident The R faces and the oo R
faces practically coincide in the twinned parts so that the crystals
resemble untwinned ones The twinning is exhibited by dull areas of
— R on bright areas of +R faces and by breaks in the continuity of the
striations on oo R
Other twinning laws have also been observed in quartz, but their
discussion as well as the more complete discussion of the mineral's
crystallization must be left for larger treatises In the most common of
these other laws the individuals are thinned about
P2(ii22). See Fig 76
The fracture of quartz is conchoidal Its hard-
ness is 7 and density 2 65 Its luster is \itreous, or
sometimes greasy Pure specimens are transparent
or colorless, but most varieties are colored by the
addition of pigments or impurities When the
coloring matter is opaque it may be present in
sufficient quantity to render the mineral also opaque ^
on. ± i IT- *• j r FlG 76— Quart!
The streak is colorless in pure varieties, and of some xwmned about
pale shade in colored varieties. The mineral is pyro- p2(n22)
electric and circularly polarizing as described above
It is an electric insulator at ordinary temperatures Its refractive
indices for yellow light are: o>= i 5443, €= i 5534
Quartz resists most of the chemical agents except the alkalies. It
dissolves in fused sodium carbonate and in solutions of the caustic
alkalies It is also soluble in HF and to a very slight degree in water,
especially in water containing small quantities of certain salts When
heated to 575° the a variety passes into the /3 variety, at 870° both
varieties pass into tndymite, and at 1470° the tndymite passes over into
cristobahte. Gradual fusion occurs just below 1470°.
The varieties of quartz have received many different names depend-
ing largely upon their color and the uses to which they are put. They
may be grouped for convenience into crystallized and crystalline vari-
eties
The principal crystallized varieties are:
164 DESCRIPTIVE MINERALOGY
Rock crystal, the colorless, transparent variety, that often forms
distinct crystals This is the variety that is used in optical instruments
It includes the Lake George diamonds, rhmestones and Brazilian peb-
bles
Amethyst, the violet-colored transparent variety.
Rose quartz, the rose-colored transparent variety.
Citrine or false topa~, a yellow and pellucid kind
Smoky quartz or Cairngorm stone, a smoky yellow or smoky brown
variety that is often transparent or translucent, but sometimes almost
opaque.
The last four varieties are used as gems, the Cairngorm stone being a
popular stone for mourning jewelry
M^lky quartz is the white, translucent or opaque variety such as so
commonly forms the gangue m mineral veins and the material of " quartz
Sag&mte is rock crystal including acicular crystals of rutile
Aventurine is rock crystal spangled with scales of some micaceous
mineral
The puncipal crystalline varieties are
Chalcedony , a very finely fibrous, transparent or translucent waxy-
looking quartz that forms mamillary or botryoidal masses Its color is
white, gray, blue or some other delicate shade The water that is always
present in it is believed to be held between the minute fibers, and not to
be combined with the silica (see also p 159)
Carnehan is the name given to a clear red or brown chalcedony
Chrysoprase is an apple-green chalcedony
Prase is a dull leek-green variety that is translucent
Plasma differs from prase in having a brighter green color and in
being translucent
Heliotrope, or lloodstone, is a plasma dotted with red spots of jasper.
All of the colored chalcedonies are used as gems or as ornamental
stones
Agate is a chalcedony, or a mixture of quartz and chalcedony , vane-
gated in color The commonest agates have the colors arranged in
bands, but there are others, like " fortification agate " in which the
colors are irregularly distributed, and still others in which the variation
in color is due to visible inclusions, as in " moss-agates " The different
bands in banded agates often differ in porosity. This property is taken
advantage of to intensify the contrast in their colors The agate is
soaked in oil, or in some other substance, and is then treated with chem-
icals that act upon the material absorbed by it Those bands which
OXIDES 165
have absorbed the greater quantity of this material become darker in
color than those that have absorbed less
On) % is a very evenly banded agate in which there is a marked con-
trast in colors Cameos are onyxes in one band of which figures are cut,
leaving another band to form a background
Sardonyx is an onyx in which some of the bands consist of carnelian.
It is usually red and white.
Flint, jasper, hornstone and touchstone are very fine grained crystalline
aggregates of gray, red or nearly black mixture of opal, chalcedony and
quartz They are more properly rocks than minerals Chert is an im-
pure flint
Sandstone is a rock composed of sand grains, most of tthich are
quartz, cemented by clay, calcite or some other substance. When the
cement is quartz the rock is a quartzite Oilstones, honestones and some
whetstones are cryptocrystalhne aggregates of quartz, very dense and
homogeneous, except for tiny rhombohedral cavities that are thought to
have resulted from the solution of crystals of calcite They are gener-
ally believed to be beds of metamorphosed chert
Syntheses — Crystallized quartz has been made in a number of ways,
both from superheated aqueous solutions and from molten magmas
Crystals have been produced by the action of water containing am-
monium fluoride upon powdered glass and upon amorphous Si02, and
by heating water in a dosed glass tube to high temperatures The
separation of crystals from molten magmas is facilitated by the addition
of small quantities of a fluoride or of tungsten compounds.
Occurrence and Origin — Quartz occurs as an essential constituent of
many crystalline rocks such as granite, gneiss, etc., and as the almost sole
component of certain sandstones It constitutes the greater portion of
most sands and the material of many veins. It also occurs as pseudo-
morphs after shells and other organic bodies embedded in rocks, having
replaced the original substance of which these bodies were composed.
It is also one of the decomposition products of many silicates. It may
thus be primary or secondary in origin. It may result from igneous or
aqueous processes, or it may be a sublimation product.
Localities — Quartz is so widely spread in its distribution that only a
very few of its most interesting localities can be referred to in this place.
The finest specimens of rock crystals come from Dauphine, France;
Carrara, in Tuscany, the Piedmont district, in Italy, and in the United
States from Middleville, and Little Falls, N. Y.; the Hot Springs,
Arkv and from several places in Alexander Co., N. C. Smoky quartz
is found in good crystals in Scotland, at Pans, Me.; in Alexander
166 DESCRIPTIVE MINERALOGY
Co , N C , and in the Pike's Peak region of Colorado The handsomest
amethysts come from Ceylon, Persia, Brazil, Nova Scotia and the
country around Lake Superior Rose quartz occurs in large quantity
at Hebron, Pans, Albany and Georgetown, Me
Fine agates and carnehans are brought from Arabia, India and Brazil.
They are abundant in the gravels of Agate Bay and of other bays and
coves on the north shore of Lake Superior
Chalcedony is abundant in the rocks of Iceland and the Faroe Islands,
in those on the northwest side of Lake Supenor, and in the gravels of
the Columbia, the Mississippi and other western rivers
The other valuable varieties of the mineral occur largely in the Far
East
Agatized, or sihcified, wood of great beauty exists in enormous quan-
tity in an old petrified forest near Cornzo, Ariz It is also found in
the Yellowstone Park, near Florissant, Colo , and in other places in the
Far West. This wood has had all of its organic matter replaced mole-
cule for molecule by quartz in such a manner that its original structure
has been perfectly preserved
Uses — Rock crystal is used more or less extensively m the construc-
tion of optical instruments and in the manufacture of cheap jewelry
Smoky quartz, amethyst, onyx, carnehan and heliotrope stones are
used as gems, and agate, prase, chrysoprase and rose quartz as orna-
mental stones
Milky quartz, ground to coarse powder, is employed in the manu-
facture of sandpaper. Its most extensive use, however, is in the man-
ufacture of glass and pottery Earthenware, porcelain and some other
varieties of potter's ware are vitrified mixtures of clay and ground
quartz, technically known as "flint " Ordinary glass is a silicate of
calcium or lead and the alkalies, sodium or potash It is made by
melting together soda, potash, lime or lead oxide and ground quartz or
quartz sand, and coloring with some metallic salt A pure quartz glass
is now being made for chemical uses by melting pure quartz sand
Quartz is sometimes used as a flux in smelting operations In the
form of sandstone, it is used as a building stone, and in the form of sand
it is employed in various building operations Bncks cut from dense
quartzites (very hard and compact sandstones) are often employed
for lining furnaces
The uses of honestones, oilstones, and whetstones are indicated by
their names.
Production — Many varieties of quartz are produced in the United
Slates to serve various uses* Vein quartz is crushed and employed
OXIDES 167
in the manufacture of wood filler, paints, pottery, scouring soaps, sand-
paper and abrasives It is also used in making ferro-silicon, chemical
ware, pottery, sand-lime brick, quartz glass, etc The total quantity
produced for these purposes in 1912 was 97,874 tons, valued at
$191,685
The largest quantity of quartz produced is in the form of sand, of
which 38,600,000 tons were marketed in 1912 at a valuation of $15,300,-
ooo Sandstone, valued at $6,900,000, was quamed for building and
paving purposes Oilstones, grindstones, millstones, etc., which are
made from special varieties of sandstone, were produced to the value of
$1,220,000
Gem quartz obtained in 1912 was valued at about $22,000. This
comprised petrified wood, chrysoprase, agate, amethyst, rock crystal,
smoky quartz, rose quartz, and gold quartz (white quartz containing
particles of gold).
THE METALLIC DIOXIDES
The metallic dioxides include the oxides of tin, titanium, manganese
and lead Of these the manganese dioxide may be dimorphous, and the
titanium dioxide is-tnmorphous. A dioxide of zirconium is also* known,
baddeleytfe, but it is extremely rare. The mineral zircon (ZrSiO4) is
often regarded as being isomorphous with cassttente (Sn02) and rutile
(Ti02) because of the similarity in the crystallization of the three min-
erals The three, therefore, are placed in the same group, in which
case all must be regarded as salts of metallic acids, thus: Ti02=TiTiO4,
SnO2=SnSn04, zircon =ZrSi04 Other authorities regard zircon as an
isomorphous mixture of Ti02 and Si02. In this book zircon is placed
with the silicates and the other minerals are considered as oxides.
The two manganese dioxides are poliantfe and pyrolusite. The former
is tetragonal and the latter orthorhombic It is possible, however, that
the crystals of pyrolusite are pseudomorphs and that the substance is a
mixture of poliamte and some hydroxide, as it nearly always contains
about 2 per cent HgO.
The three titanium oxides are ridde, which is tetragonal; brookitc,
which is orthorhombic, and anatase or octakednte, which is tetragonal.
Although rutile and anatase crystallize in the same system, their axial
ratios are different, as are also their crystal habits and their physical
properties. A few of these differences are indicated below:
Rutde a:c=i: .6439; Sp. Gr. =4-283; «»= 2.6158; $«= 2.9029.
Anatase -1:1.7771; Sp. Gr. =3.9 ; ^=2.5618; ^=2.4886.
168 DESCRIPTIVE MINERALOGY
Of the tliree modifications of titanium dioxide, anatase may be
made at a comparatively low temperature Brookite requires a higher
temperature for its production, but rutilfc is producible at both high
and low temperatures Under the conditions of nature both brookite
and anatase pass readily into rutile
Of the seven dioxides discussed, four are members of a single group
RUTILE GROUP
The rutile group consists of four minerals apparently completely
isomorphous, though no mixed crystals of any two have been discovered :
All crystallize in the tetragonal system (ditetragonal bipyramidal class),
with the same forms and with closely corresponding axial ratios The
names of the members of the group and their axial ratios follow
Cassitente (Sn02) a • c =i . 6726
Ruttle (Ti02) =i • 6439
Pohamte (Mn02) =i ' 6647
Plattnente (PbOa) =i ' 6764
Cassiterite (Sn02)
Cassiterite, or tinstone, is the only worked ore of tin It occurs as
rolled pebbles of a dark brown color in the beds of streams, as fibrous
aggregates, and as ghstemng black crystals associated with other min-
erals in veins
The analyses of cassitente indicate it to be essentially an oxide of
tin, or, possibly, a stanyl stannale ((SnOJSnOa), with the composition,
Sn=78.6 per cent; 0=2i 4 per cent. The mineral nearly always con-
tains some iron oxide and often oxides of tantalum, of zinc or of arsenic
The presence of iron and tantalum is so general that most crystals of
cassitente may be regarded as isomorphous mixtures of (SnO)(SnOs);
Fe(SnOs) and Fe(TaOs)2- Thus, a crystal from the Etta Mine in the
Black Hills, S. D, gave Sn02=9436; FeO-i62, Ta205=242 and
8102=100, indicating a mixture of 5 pts of Fe(TaOs)2, 18 pts. of
Fe(SnOs) and 303 5 pts of (SnO)(SnOs).
The crystals of cassitente have an axial ratio of i : ,6726. They are
usually short prisms in habit They often consist of the simple com-
bination P(in) and POO(IOI) (Fig 77), or of these forms, together
with sPf (321) and various prisms (Fig 78). Twins are common, the
1An isomorphous mixture of the rutile and cassitente molecules has recently
been described from Greifenstem, Austria, but its existence has not yet been con-
firmed
OXIDES
169
twinning plane being P oo (101) When the individuals twinned have
small prismatic faces the resulting combination is often called a visor
twin (Fig 79), because of its supposed resemblance to the vitor of a
helmet By repetition of the twinning very complex groupings are
produced The angle in A * ^* — 58° 19'
FIG 77 FIG 78
FIG. 77. — Cassitente Crystal with P, m (s) and P * , 101 fc)
FIG 78.— Cassitente Crystal with s, e and °o P, no (m), «o P2, 210 (A), 3pJ, 321 (=).
The cleavage of cassitente is imperfect parallel to oo P oo (100) and
P(III) Its fracture is uneven The color of the massive mineral is
some dark shade of brown by reflected light, and of the crystals black
By transmitted light, the mineral is brown or black Its luster is very
brilliant, and its streak is white, gray or brown. The purest specimens
FIG 79 —Cassitente Twinned about P «5 (101), o=ooPoo,ioo A=*VisorTwin.
are nearly transparent, though the ordinary varieties are opaque Their
hardness is about 6 5 and density about 7 The mineral is a noncon-
ductor of electricity Its refractive indices for yellow light are: w = 1 9965,
6=2.0931.
Three varieties of cassitente are recognized, distinguished by physical
characteristics The ordinary variety known as tinskme is crystallised
170 DESCRIPTIVE MINERALOGY
or massive. Wood tin is a botryoidal or remform variety, concentric in
structure and composed of radiating fibers The third variety is stream
tin This consists of water-worn pebbles found m the beds of streams
that flow over cassitente-bearmg rocks
Cassitente is only slightly acted upon by acids It may be reduced
to a metallic globule of tin only with difficulty, even when mixed
with sodium carbonate and heated intensely on charcoal. With
borax it yields slight reactions for iron, manganese or other impurities
When placed in dilute hydrochloric acid with pieces of granulated zinc,
fragments of cassiterite become covered with a dull gray coating of
metallic tin which can be burnished by rubbing with a doth or the hand
When rubbed by the hand the odor of tin in contact with flesh is easily
detected.
The mineral is most easily distinguished from other compounds that
resemble it in appearance by its high density and its inertness when
treated with reagents or before the blowpipe
Syntheses —Crystals of cassiterite have been obtained by passing
steam and vapor of tin chloride or tin fluoride through red-hot porcelain
tubes, and by the action of tin chloride \apor upon lime
Occurrence and Origin. — Tinstone is found as a primary mineral in
coarse granite veins with topaz, tourmaline, fluorite, apatite and a great
number of other minerals It also occurs impregnating rocks, sometimes
replacing the minerals of which they originally consisted. In these
cases it is the product of pneumatolytic processes. In many places it
constitutes a large proportion of the gravel in the beds of streams
Localities and Production — The crystallized mineral occurs at many
places in Bohemia and in Saxony, at Limoges in France and sparingly
in a few places in the United States, especially near El Paso, Texas,
in Cherokee Co., N. C , in Lincoln Co , S C , and near Hill City, S D
Massive tinstone and stream tin occur in laige enough quantities to be
mined in Cornwall, England, on the Malay Peninsula and on the islands
lying off its extremity; in Tasmania; in New South Wales, Victoria
and Queensland, Australia; in the gold regions of Bolivia, at Durango
in Mexico, and at various points in Alaska, at some of which there,
are 400 Ib. of cassiterite in a cubic yard of gravel.
The principal tin ore-producing regions of the world are the Straits,
district, including the Malay Peninsula and the islands of the Malay
Archipelago; Australia; Cornwall, England, the Dutch East Indies, and
Bolivia* Of the total output of 122,752 tons of tin produced m 1911,
61,712 tons were made from the Straits ore, 25,312 tons from the ore
produced in Bolivia and 16,800 tons from Banka ore. Of the total
OXIDES
171
quantity of tin produced about 78 per cent is said to come from stream
tin and 22 per cent from ore obtained from veins. The quantity
obtained from ore mined in the United States in igu included 61 tons
from Alaskan stream tin and two tons from the tinstone mined in the
Franklin Mountains near El Paso, Texas Mines have been opened in
San Bernardino Co , California, and in the Black Hills, South Dakota,
but they have not proved successful The mines at El Paso, Texas, are
not yet fully developed, although they promise to be profitable in the
near future The crystals are scattered through quartz veins and
through a pink granite near the contacts with the veins The average
composition of the ore is 2 per cent This is concentrated to a 60 per
cent ore before being smelted The production during 1912 was 130
tons of stream tin from Buck Creek, Alaska This was valued at
$124,800. In the following year 3 tons of cassitente ^ere shipped from
Gaffney, S C The imports of tin into the United States during 1911
were 53,527 tons valued at more than $43,300,000
Enaction — The tin is extracted from the concentrated ore by the
simple process of reduction Alternate layers of the ore and charcoal
are heated together in a furnace, when the metal results This collects
in the bottom of the furnace and is ladled or run out The crude metal is
refined by remeltmg m special refining furnaces
Uses of the Metal — The metal tin is employed principally for coating
other metals, either to prevent rusting or to pre\ent the action upon
them of chemical reagents Tin plate is thin sheet iron covered with
tin Copper for culinary purposes is also often co\ ered with this metal
It is used also extensively in forming alloys with copper, antimony,
bismuth and lead Among the most important of these alloys are
bronze, bell metal, babbitt metal, gun metal, britanma, pewter and soft
solder Its alloy, or amalgam, with mercury is used in coating mirrors.
Several of its compounds also find uses m the arts Tin oside is an im-
portant constituent of certain enamels The chlorides are used exten-
sively in dyeing calicoes, and the bisulphide constitutes " bronze
powder " or " mosaic gold," a powder employed for bronzing plaster,
wood and metals
Rutile (Ti02)
Rutile is one of the oxides of the comparatively rare element titanium.
It occurs commonly m dark brown opaque cleavable masses and in bril-
liant black crystals
Pure rutile consists of 40 per cent 0 and 60 per cent TL Nearly all
specimens, however, contain in addition some iron, occasionally as much
172
DESCRIPTIVE MINERALOGY
as 9 per cent or 10 per cent, which is probably due to the admixture of
and FeTiOs in solid solution
Rutile is perfectly isomorphous with cassiterite Its axial ratio is
i : 6439 The pnncipal planes observed on its crystals are practically
the same as those observed on cassiterite (Fig 80) Twins aie common,
with P oo (101) the twinning plane (Fig 81 ) This twinning is often
repeated, producing elbow-shaped groups (Fig 82), or by further repe-
FIG So.— Rutile Crystals with «o P, no (m), oo p oo , 100 (a), P oo , yoi (e), P, 111(5),
«>P3> 3io (0, p3» 313 (0 and 3PJ, 321 00
FIG 81
FIG 82
FIG 81 —Rutile Eightling Twinned about P oo (101)
FIG 82 —Rutile Twinned about P oo (101) Elbow Twin
tition wheel-shaped aggregates (Fig 83) In another common law the
twinning plane is 3? oo (301") (Fig 84) The angle in A iTx — 56° 52^'
The crystals are prismatic and even sometimes acicular in habit. Their
prismatic planes are vertically striated
The cleavage of rutile is quite distinct parallel to oo P(no) and less
so parallel to oo P oo (100)
The mineral is reddish brown, yellowish brown, black or bluish
brown by leflected light and sometimes deep red by transmitted light,
Many specimens are opaque but some are translucent to transparent.
OXIDES
173
The latter are often pleochroic in tints varying between yellow and
blood-red The streak is pale brown The hardness of the mineral is
6 to 6 5 and its density about 42 It is an electric nonconductor at
ordinary temperatures Its refractive indices for yellow light are:
o>= 2 6030, €=2 8894.
Rutile is infusible and insoluble. Its reactions with beads of borax
and microcosmic salt are usually obscured by the iron present When
this metal is present only in small quantities the microcosmic salt bead
is colorless while hot, but violet when cold, if it has been heated for some
time in the reducing flame of the blowpipe
The most characteristic chemical reaction of rutile is obtained upon
fusing it with sodium carbonate on charcoal, dissolving the fused mass in
FIG 83. FIG 84
FIG 83 —Rutile Cyclic Sixling Twinned about P « (101)
FIG 84 — Rutile Twinned about 3? » (301) Elbow Twin Forms °° P2, 210 (A),
and P °o , ioi (e)
an excess of hydrochloric acid and adding to the solution small scraps of
tin Upon heating for some little time, the solution assumes a violet
color. This is a universal test for the metal titanium
Some of the dark red and reddish brown massive varieties of rutile
may be confounded with some varieties of garnet, which, however, are
much harder. Its density, its infusibihty and the reaction for titanium
serve to characterize the mineral perfectly
Pseudomorphs of rutile after hematite and after brookite and ana-
tase have been described It often changes into ilmenite and sphene.
Syntheses. — By the reaction between TiCU and water vapcr in a red-
hot porcelain tube, crystals of rutile are formed. Twins are produced
by submitting precipitated titanic acid in a mass of molten sodium tung-
state to a temperature of 1000° for several weeks.
Occurrence and Origin —Rutile is often found as crystals embedded
in limestone and m the quartz or f eldspar of granite and other igneous
174 DESCRIPTIVE MINERALOGY
rocks, as long acicular crystals m slates, and as grams in the rock known
as nelsomte It occurs also as fine hair-like needles penetrating quartz,
forming the ornamental stone " fleches d'amour," and as grains in the
gold-bearing sand regions When primary it is probably always a
product of magmatic processes, either crystallizing from a molten magma
or being the result of pneumatolysis.
Localities — Handsome crystals of the mineral occur at Arendal, in
Norway, in Tyrol, and at St Gothard and in the Binnenthal, Switzer-
land In the United States large crystals have been obtained at Barre,
Mass , at Sudbury, Chester Co , Penn ; at Stony Point, Alexander Co ,
N C , at Graves Mt , in Georgia, at Magnet Cove, in Arkansas, and
in Nelson Co , Va. In the latter place it occurs in large quantity as
crystals disseminated through a coarse granite rock The rock con-
taining about 10 per cent of rutile is mined as an ore It constitutes the
principal source of the mineral in the United States A second type
of occurrence in the same locality is a dike-like rock, nelsomte, composed
of ilmemte and apatite, in which the ilmemte is in places almost
completely replaced by rutile
Uses — The mineral is not of great economic importance It is used
in small quantity to impart a yellow color to porcelain and to give an
ivory tint to artificial teeth. It is also used in the manufacture of the
alloy ferro-titamum which is added to steel to increase its strength
Recently the use of titamferous electrodes in arc lights, and the use of
titanium for filaments in incandescent lamps ha\e been proposed Some
of the salts of titanium are used as dyes and others as mordants Most
of the ferro-titamum made m the United States is manufactured from
titamferous magnetite
Production — The only rutile mined in the United States during 1913
came from Roseland, Nelson Co., Virginia. It amounted to 305 tons of
concentrates containing about 82 per cent TiOs At the same time there
were separated about 250 tons of ilmemte (see p 462)
Polianite (MnC^I is usually in groups of tiny parallel crystals and
as crusts of crystals enveloping crystals of manganite (MnO OH). Their
axial ratio is i ' 6647 The color of the mineral is iron-gray. Its streak
is black, its hardness 6-6 5 and density 4 99. It dissolves in HC1 evolv-
ing chlorine It is distinguished from pyrolusite by its greater hardness
and its lack of water The mineral is extremely rare, being found in
measurable crystals only at Platten in Bohemia It occurs in pseudo-
morphs after manganite at a number of other points m Europe and at a
few points elsewhere, but in most cases it has not been dearly distin-
OXIDES 175
guished from pyrolusite The rarity of its crystals is regarded by some
mineralogists as being due to the fact that in most of its occurrences
poliamte is colloidal (a gel)
Plattnerite (PbO2) is usually massive, but it occurs in prismatic
crystals near Mullan in Idaho Their axial ratio is i : 6764 They are
usually bounded by oo P oo (100), 3? oo (301), P oo (101), oP (ooi) and
often IP (33 2) The mineral is found also in crusts Its color is
iron-black and its streak chestnut-brown Its hardness is 5-5 5 and
its density 86 It is brittle and is easily fusible before the blow-
pipe, giving off oxygen and coloring the flame blue It yields a lead
bead It is difficultly soluble in HNOs, but easily soluble in HC1 with
evolution of chlorine. Plattnente is found at Leadhills and at Wanlock-
head, Scotland, and at the " As You Like " Mine near Mullan, Idaho.
Pyrolusite
Pyrolusite is often the result of the alteration of the hydroxide, man-
gamte, or of pohamte. The few measurable crystals that have been
studied seem to indicate that their form is pseudomorphic after the
hydroxide The change by which manganite may pass over into pyro-
lusite is represented by the reaction 2MnO(OH)-f-0=2Mn02+H2O.
Pyroiusite may be, however, only a slightly hydrated form of poliamte.
An analysis of a specimen from Negaunee, Mich., gave
MnO O CaO BaO SiOa Limomte HgO Total
79 46 17 48 18 38 18 .31 i 94 99 93
Pyrolusite, as usually found, is in granular or columnar masses, or in
masses of radiating fibers It is a soft, black mineral with a hardness of
only 2 or 2 5 and a density of about 4.8 Its luster is metallic and its
streak black It is a fairly good conductor of electricity.
The reactions of this mineral are practically the same as those of
pohanite and manganite (see p 191), except that only a small quantity
of water is obtained from it by heating. Upon strong heating it yields
oxygen, according to the equation 3Mn02=Mn3+3Q2-
The manganese minerals are easily distinguished from other minerals
by the violet color they give to the borax bead and by the green prxjduct
obtained when they are fused with sodium carbonate. Pyrolusite is
distinguished from manganite by its physical properties, and from
amte by its softness
176 DESCRIPTIVE MINERALOGY
Localities — -Pyrolusite is worked at Elgersberg, near Ilmenau in
Thuringia, at Vorder Ehrensdorf in Moravia, at Flatten in Bohemia,
at CartersviUe, Ga , at Batesville, Ark , and m the Valley of Virginia
A manganiferous silver ore containing considerable quantities of pyro-
lusite is mined in the Leadville district, Colorado, and large quan-
tities of manganiferous iron ores are obtained in the Lake Superior
region
Uses — Pyrolusite, together with the other manganese ores with
which it is mixed, is the source of nearly all the manganese compounds
employed in the arts Some of the ores, moreover, are argentiferous
and others contain zinc From these silver and zinc are extracted The
most important use of the mineral is in the iron industry. In this indus-
try, however, much of the manganese employed is obtained from man-
gamferous iron ores The alloys spiegeleisen and ferro-manganese are
employed very largely in the production of an iron used m casting car
wheels. It is extremely hard and tough The manganese minerals are
also used in glass factories to neutralize the green color imparted to glass
by the ferruginous impurities m the sands from which the glass is made
They are also used m giving black, brown and violet colors to pottery
and some of their salts are valuable mordants Pyrolusite, finally, is the
principal compound by the aid of which chlorine and oxygen are pro-
duced.
Production — The United States in 1912 produced about 1,664 tons
of manganese ores, valued at $15,723, and all came from Virginia, South
Carolina and California In previous years the ores had been mined
also m Arkansas, Tennessee and Utah Moreover, there were imported
into the country 300,661 tons, valued at $1,769,000 Nearly all of this
was used in the manufacture of spiegeleisen The domestic product was
used in the chemical industries largely in the manufacture of manganese
brick Of the manganiferous iron ores about 818,000 tons were produced
ui 1912 These were utilized mainly as ores of iron, though a large por-
tion was used as a flux. The product of manganiferous silver ores aggre-
gated about 48,600 tons, all of which was used as a flux for silver-lead
ores. Nearly all of this came from Colorado In addition there were
imported iron-manganese alloys valued at $3,935,000.
Anatase and BrooMte
As has already been stated, the compound Ti02 is trimorphous, one
form being orthorhombic and the two others tetragonal Of the latter,
one has already been described as rutile The other is anatase, or octa-
hednte. The orthorhombic form is known as brookite Anatase and
OXIDES 177
rutile are separated because of the difference in their axial ratios and in
the habits of their crystals Both are ditetragonal bipyramidal, but
a : c for rutile is i : 6439 and for anatase i . i 7771 Brookite is
orthorhombic bipyramidal with a : b • c- 8416 : i : .9444.
Both anatase and brookite have the same empirical composition,
which is similar to that of rutile
Crystals of anatase are usually sharp pyramidal with the form P(in)
predominating (Fig 85), blunt pyramidal with |P(ii3) or $P(ii7)
predominating (Fig 86), or tabular parallel to oP(ooi) Twins are
common in some localities, with P oo (101) the twinning plane. The
angle in A iTiaBS82° 91'
The mineral is colorless and transparent, or dark blue, yellow, brown
FIG 86
FIG 85 — Anatase Crystal with P in (p)
FIG 86— Anatase Crystal with fP, 113 (s), P, in (p), IP, 117 fr); °°P» «o (*»),
oo P oo , 100 (a) and P GO , 101 (t)
or nearly black and almost opaque Its streak is colorless to light
yellow. Its cleavage is perfect parallel to P and oP and its fracture
conchoidal Its hardness is between 5 and 6 and its density is 3.9. This
increases to 4 25 upon heating to a red heat, possibly due to its partial
transformation into rutile The mineral is insoluble in acids except
hot concentrated EkSO-i. It is a nonconductor of electricity. Its
indices of refraction for yellow light are w= 2 5618, e= 2 4886
Brooktte crystals are usually tabular parallel to oo P 60 (too) and
elongated in the direction of the c axis Nearly all crystals are
striated in the vertical zone Although many forms have been identi-
fied on them, by far the most common is P2(i22) In some cases this is
the only pyramidal form present, as in the type known as arkanstie
(Fig. 87) Twins are rare, with oo ¥2(210) the twinning plane. The
angle in AiTi==:640 17'.
178
DESCRIPTIVE MINERALOGY
Brookite may be opaque, translucent or transparent Its color
vanes from yellowish brown, through brownish red, to black (arkansite)
Its streak is brownish yellow Its clea\age is imperfect parallel to
oo Poo (101), and its fracture uneven or conchoidal Its hardness is
5-6 and density about 4, Upon heating its density increases to that of
rutile Its refractive indices for yellow light are a= 2 5832, #= 2 5856,
7=2 7414 It fuses at about 1560°, and is insoluble in acids
The chemical properties of both brookite and anatase are similar
to those of rutile They are distinguished from rutile by their physical
properties and their crystallization
Both brookite and anatase alter to rutile
Syntheses —Upon heating TiFi with water vapor at a temperature
FIG §7— Brookite Crystals with coP, no (w), JP, 112 (z) and PsT, 122 (e)
combination m and e is characteristic for \rkanbitc
The
below that of vaporizing cadmium, crystals of anatase are produced.
If the temperature is raised above the point of vaporization of cadmium
and kept below that of zinc, crystals of brookite result
Occurrence — Brookite and anatase occur as crystals on the walls of
clefts in crystalline silicate rocks and in weathered phases of volcanic
rocks. They are mainly pneumatolytic products, the production of the
one or the other depending upon the temperature at which the TiCfe was
deposited
Localities — Fine brookite crystals are found at St Gothard, in
Switzerland, at Pregrattan, in the Tyrol, near Tremadoc, in Wales,
at Miask, in Russia, and at Magnet Cove, Arkansas
Anatase crystals are less common than those of brookite but they
occur at many points in Switzerland, especially in the Binnenthal,
near Bourg d'Oisans, France, at many points in the Urals, Russia, in
the diamond fields of Brazil, and at the brookite occurrences m Arkansas,
CHAPTER VIE
*
THE HYDROXIDES
THE hydroxides, as has already been explained, may be looked upon
as derivatives of water, m which only a portion of the hydrogen has been
replaced. The group includes several minerals of economic importance,
among which is the fine gem mineral opal All the hydroxides yield
water when heated in a glass tube, but they do not yield it as readily as
do salts containing water of crystallization
A few of the hydroxides may act as acids forming salts with metals
Diaspore, for instance, is an hydroxide of aluminium A10-OH, or
/0-H
Al< , which appears to be able to form salts, at least, the chemical
composition of some of the members of an important group of minerals,
the spinels, may be explained by regarding them as salts of this acid
(seep 195)
Opal (Si02+Aq)
The true position of opal in the classification of minerals is somewhat
doubtful From the analyses made it appears to be a combination of
amorphous silica and water, or, perhaps, a mixture of silica in some form
and a hydroxide of silicon The percentage of water present is variable.
In some specimens it is as low as 3 per cent, while in others it is as high
as 13 per cent The mineral is not known in crystals. It is probably a
colloid, in which the water is, in part at least, mechanically held in a gel
of SiCfe. It occurs only m massive form, in stalactitic or globular masses
and in an earthy condition.
When pure the mineral is colorless and transparent Usually, how-
ever, it is colored some shade of yellow, red, green or blue, when it is
translucent or sometimes even opaque. The red and yellow varieties con-
tain iron oxides and the green, prasopd, some nickd compound The
play of color in gem opal is due to the interference of light rays reflected
from the sides of thin layers of opal material with different densities
from that of the mam mass of the mineral they traverse. The hardness
of opal is 5 5-6 $ and its density about 2.1 Its refractive index for
yellow light, n= 1.4401, It is a nonconductor of electricity.
179
180 DESCRIPTIVE MINERALOGY
The principal varieties of opal are
Precwus opal, a transparent variety exhibiting a delicate play of
colors,
Fire opal, a precious opal in which the colors are quite brilliant
shades of red and yellow,
Girasol, a bluish white translucent opal with reddish reflections,
Common opal, a translucent variety without any distinct play of
colors,
Cachalong, an opaque bluish white, porcelain-like variety,
Hyalite, a transparent, colorless variety, usually m globular or
botryoidal masses, and
Siliceous sinter, white, translucent to opaque pulverulent accumula-
tions and hard crusts, deposited from the waters of geysers and other
hot springs.
Tnpolite and infusorial earth are pulverulent forms of silica in which
opal is an important constituent Tripoli is a light porous siliceous
rock, supposed to have resulted from the leaching of calcareous material
from a siliceous limestone Infusorial earth represents the remains of
certain aquatic forms of microscopic plants known as diatoms
Flint and Chert are mixtures of opal, chalcedony and quartz
All vaneties of opal are infusible and all become opaque when heated
When boiled with caustic alkalies some varieties dissolve easily, while
others dissolve very slowly.
Syntheses — Coatings of material like opal have been noted in glass
flasks containing hydrofluosilicic acid that had not been opened for
several years Opal has also been obtained by the slow cooling of a
solution of silicic acid in water.
Occurrence — The mineral occurs as deposits around hot springs
It also forms veins in volcanic rocks and is embedded in certain lime-
stones and slates, where it is probably the result of the solution of the
siliceous spicules and shells of low forms of Me and subsequent deposi-
tion It also results from the solution of the calcite from limestones
containing finely divided silica
It is not an uncommon alteration product of silicates It seems to
have been deposited from both cold and hot water
Localities. — Precious opal is found near Kashan, in Hungary, at
Zimapan, Quaretaro, in Mexico, in Honduras, in Queensland and
New South Wales, Australia, and in the Faroe Islands Common opal is
abundant at most of these localities and is found also in Moravia,
Bohemia, Iceland, Scotland and the Hebrides Hyalite occurs in small
quantity at several places m New York, New Jersey, North Carolina,
HYDROXIDES 181
Georgia and Florida, and common opal, at Cornwall, Perm., and in
Calaveras Co , California Common opal and vaneties exhibiting a little
fire have recently been explored in Humboldt and Lander Counties,
Nevada Siliceous sinter is deposited at the Steamboat Springs in
Nevada and geysente (a globular form of the sinter) at the mouths of the
geysers in the Yellowstone National Park
Uses — The precious and fire opals are popular and handsome gems
Opahzed wood, i e , wood that has been changed into opal in such a
manner as to retain its woody structure, is often cut and polished for use
as an ornamental stone Infusorial earth, a white earthy deposit of
microscopic shells consisting largely of opal material, possesses manv
uses It is employed in the manufacture of soluble glass, polishing
powders, cements, etc , and as the " body," which, saturated with nitro-
glycerine, composes dynamite, Tripoli, a mixture of quartz and opal,
is used as a wood filler, in making paint, as an abrasive and in the
manufacture of filter stones. The principal sources of commercially
valuable opal material in the United States are the opalized forest in
Apache Co., Ariz , the infusorial earth beds at Pope's Creek and Dun-
kirk, Md , various places in Napa Co , Cal , at Virginia City, Nev ,
and at Drakesville, N. J., and the tnpoh beds in the neighborhood of
Stella, Mo , and the adjoining portion of Illinois
Production — The total quantity of infusonal earth and tnpoh mined
during 1912 was valued at $125,446. The aggregate value of precious
opal obtained in 1912 was $10,925. TluTcame from California and
Arizona.
Brucite (Mg(OH)2)
Brucite is the hydroxide of magnesium. It is a white, soft mineral
usually occurring in crystals or in foliated masses
Analyses of the mineral correspond very closely to the formula
Mg(OH)2 which requires 41 38 per cent Mg, 27 62 per cent 0 and 31.00
per cent EkO, though they usually show the presence of small quantities
of iron and manganese A specimen from Reading, Perm., yielded:
MgO F^O3 MnO H2O Total
67.64 82 63 3° 92 I0° OI
The crystallization of brucite is hexagonal (ditrigonal scalenohedral),
a : c=i : 1.5208 The crystals are tabular in habit in consequence of
the broad development of the basal plane oP(oooi). The other forms
present are R(ioli), -^(0441) and -fRCoiTj) (Fig. 88) The angle
roll A 7ioi = 97° 38'.
182 DESCRIPTIVE MINERALOGY
The cleavage of brucite is very perfect parallel to oP(ooi), and folia
that may be split off are flexible The mineral is sectiie Its hardness
is 2 5 and its density 2 4 Its color is white, inclining to bluish and
greenish tints, and its luster pearly on oP Brucite is transparent to
translucent It is pyroelectnc and a non-
conductor of electricity Its refractive indices
for red light are «« i 559» €== * 579
In the closed tube brucite, like other hy-
droxides, yields water The mineral is infusi-
ble When intensely heated, it glows After
FIG 88 —Brucite Crystal heating, it reacts alkaline When moistened
with oR, ocoi (<0, R, mfo cobalt mtrate solution and heated, it turns
Pmk» the characterlstlc reaction for magnesium
The pure mineral is soluble in acids
Brucite resembles m many respects gypsum, talc, diaspore and some
micas It is distinguished from diaspore and mica by its hardness and
from talc by its solubility in acids Gypsum is a sulphate, hence the
test for sulphur will sufficiently characterize it
Synthesis — Crystals have been made by precipitating a solution of
magnesium chloride with an alcoholic solution of potash, dissolving the
precipitate by heating with an excess of KOH and allowing to cool
Occurrence and Origin — Brucite is usually associated with other
magnesium minerals It is often found in veins cutting the rock known
as serpentine, where it is probably a weathering product, and is some-
times found in masses in limestone, especially near its contact with
igneous rocks
Localities — It occurs crystallized in one of the Shetland Islands, at
the Tilly Foster Iron Mine, Brewster, N Y , at Woods Mine, Texas,
Perm , and at Fritz Island, near Reading, in the same State
Gibbsite (A1(OH)3)
Gibbsite, or hydrargillite, is utilized to some extent as an ore of alu-
minium It occurs as crystals, in granular masses, in stalactites and in
fibrous, radiating aggregates
Its theoretical composition demands 6541 per cent AkOs and
34.59 per cent H20 Usually, however, the mineral is mixed with bauxite
(AlsO(OH)4) and in addition contains also small quantities of iron,
magnesium, silicon and often calcium
Crystals are monodmic with a : b : 1=1.709 * i : i 918 and £=85°
29!'. Their habit is tabular, Besides the basal plane, oP(ooi), the
HYDROXIDES 183
two most prominent forms are so Poo (I00) ancj aop(IIOi Thus the
plates have hexagonal outlines They ha\e a perfect cleavage parallel
to the base Twinning is common, \\ith oP(ooi) the twinning plane
The mineral has a glass} luster except on the basal plane where its
luster is pearly It is transparent or translucent, Tvhite, pink, green or
gray Its streak is light, its hardness is 2-3 and specific gravity 2 35
It is a nonconductor of electricity. Its refractue indices are a =8
= 15347, 7=15577
When heated before the blowpipe the mineral exfoliates, becomes
white, glows strongly but does not fuse Upon cooling the heated mass
is hard enough to scratch glass The mineral dissolves slowly but com-
pletely m hot HC1 and in strong HaSOi, and gives a blue color when
moistened with Co(NOs)2 solution and heated.
Gibbsite resembles most closely bauxite, from which it is distin-
guished principally by its structure It differs from umelhte (p. 287),
which it also sometimes resembles, in the absence of phosphorus.
Syntheses — Crystals of gibbsite have been made b\ heating on a
water bath a saturated solution of Al(OH)s in dilute ammonia until all
of the ammonia evaporates, and also by gradually precipitating the
hjdroxide from a warm alkaline solution by means of a slow stream
ofCO2
Occurrence — The mineral rarely occurs in pure form It is found in
veins and in cavities in various schistose and igneous rocks. It is prob-
ably a weathering product of aluminous silicates.
Localities — Gibbsite has been reported as existing in small quantities
at various points m Europe, near Bombay, India, and at several places
in South America and Africa. In the United States it occurs at Rich-
mond, Mass , at Union Vale, Dutchess Co , N Y., and mixed with
bauxite at several of the occurrences of this mineral (see page 186).
Uses. — It is mined with bauxite as a source of aluminium.
Limonite (Fe4O3(OH)b)
Limomte is an earthy or massrve reddish brown mineral whose
composition and crystallization are but imperfectly known It is an
important iron ore called in the trade " brown hematite "
The analyses of limomte range between wide limits, largely because
of the great quantities of impurities mixed with it. The formula de-
mands 59 8 per cent Fe, 25 7 per cent 0 and 14.5 per cent water, but the
percentages of these constituents found in different specimens only
approximately correspond to these figures Many mineralogists regard
184
DESCRIPTIVE MINERALOGY
Fte 89 — Limonite Stalactites in Silverbow Mine, Butte, Mont (After W H Weed )
Era 90— Botiyoidal Lunomte
HYDROXIDES 185
limomte as colloidal goethite (FeO OH > with one molecule or more of
EfeO, depending upon temperature The principal impurities are clay,
sand, phosphates, silica, manganese compounds and organic matter
The great variety of these is thought to be due to the lact that the
hmonite, like other gels, possesses the po\\er of absorbing compounds
from their solution, so that the mineral is in reaht> a mixture of col-
loidal iron h\ dro\ide and \ anous compounds which differ in different
occurrences
The mineral occurs in stalactites (Fig 8g\ in botiyoidd forms tFig
90), in concretionary and clay-like masses and often as pseudomorphs
after other minerals and after the roots, lea\es and stems of trees
Limomte is brown on a fresh fracture, though the surface of mc.ny
specimens is co\ ered \uth a black coating that is so lustrous as to appear
varnished Its streak is yellowish brown Its hardness is a little o\ er
5 and its density about 3.7. The mineral is opaque and its luster is dull,
silky or almost metallic according to the ph\sical conditions of the spec-
imen. Its index of refraction is about 25 It is a nonconductor of
electricity
The varieties recognized are. compact, the stdactitic and other
fibrous forms, ocherous, the brown or yellow ecrthy, impure variety,
bog iron^ the porous variety found in marshes, pseudomorphing leaves,
etc , and brown clay ironstone, the compact, massive or nodular
form.
In its chemical properties limomte resembles goer tie, from ^hich it
can be distinguished only with great difficulty except when the latter is
in crystals From uncrystalhzed varieties of goethite it can usually be
distinguished only by quantitative analysis, although in pure specimens
the streaks are different
Occurrence and Origin. — Limonite is the usual result of the decom-
position of other iron-bearing minerals Consequently, it is often found
in pseudomorphs. In almost all cases 'ahere large beds of the ore occur
the material has been deposited from ferriferous water nch in organic
substances One of the commonest types of occurrence is " gossan."
In the production of this type of ore, those portions of veins carrying
ferruginous minerals are oxidized under the influence of oxygen-bearing
waters, forming a layer composed largely of limonite which covers the
upper portion of the veins and hides the original vein matter Gossan
ores denved from chalcopynte and pynte are common in all regions in
which these minerals occur Another type of limonitic ore comprises
those found in clays derived from limestones by weathering In such
deposits the ore occurs as nodules and in pockets in the day. Ores of
186 DESCRIPTIVE MINERALOGY
this type are common in the valleys within the Appalachian Moun-
tains Bog iron ores occur in swamps and lakes into which ferruginous
solutions drain The iron may come from pynte or iron silicates in the
drainage basins of the lakes or swamps When carried down it is oxi-
dized by the air and sinks to the bottom
Localities —The mineral occurs abundantly and in many different
localities The most important American occurrences are extensive
beds at Salisbury and Kent, Conn , at many points in New Jersey,
Pennsylvania, Michigan, Tennessee, Alabama, Ohio, Virginia and
Georgia
Uses — Although containing less iron than hematite, on account of
its cheapness, and the ease with which it works in the furnace, brown
hematite is an important ore of this metal The earthy \arieties are
used as cheap paints
Production —The yield of the United States " brown hematite "
mines for 1912 was a little over 1,600,000 tons Of this amount the
largest yields were
Alabama 749,242 tons
Virginia 398,833 tons
Tennessee 171,130 tons
The quantity of ocher produced in the United States during the same
year amounted to about 15,269 tons, valued at $149,289 Most of it
came from Georgia In addition, 8,020 tons were imported. This
had a value of $148,300
Bauxite (A12O(OH)4)
Bauxite, or beauxite, like hmomte, is probably a colloid At any
rate it is unknown in crystals Until recently it possessed but little
value It is now, however, of considerable, importance as it is the prin-
cipal source of the aluminium on the market
The mineral is apparently an hydroxide of aluminium with the for-
mula Al20(OH)4 or Al20s 2H20 m which 26 i per cent is water and
73 9 per cent alumina (Al20s), but it may be a colloidal mixture of the
gibbsite and diaspore (p 190) molecules, or of various hydroxides,
since its analyses vary within wide limits A sample of very pure
material from Georgia gave on analysis
A12O3 Fe203 Si02 Ti02 H2O
62 46 81 4 72 23 31 o^
HYDROXIDES
1ST
Bauxite occurs in concretionan grains (Fig 91*, m earthy, clay-like
forms and massu e, usually in pockets or lenses in cia\ resulting from the
weathering of limestones or of s\emte It is \\hite when pure, but as
usually found is yellow, gra> , red or brown in color, is translucent to
opaque and has a colorless or very light streak. Its densitx is 2 55
and its hardness anywhere between i and 3 Its luster is dull. It is
a nonconductor of electricity
Before the blowpipe bauxite is infusible In the closed'tube it yields
FEG. 91 — Pisohtic Bauxite, from near Rock Run, Cherokee Co , Ala.
water at a high temperature. Its powder when intensely heated with a
few drops of cobalt nitrate solution turns blue. The mineral is with
difficulty soluble in hydrochloric acid.
Occurrence and Origin —Bauxite in some cases may be a deposit from
hot alkaline waters, but in Arkansas it is a residual ^eathenng product
of the igneous rock, syenite. It occurs in beds associated with corundum,
clay, gibbsite and other aluminium minerals.
Localities. — Large deposits of the ore occur at Baux, near Aries,
France, near Lake Wochem, in Carniola, in Nassau; at Antrim, Ire-
land, in a stretch of country between Jacksonville, Fla., and Carters-
188 DESCRIPTIVE MINERALOGY
ville, Ga , in Saline and Pulaski Counties, Ark , m Wilkinson Co , Ga ,
and near Chattanooga, Tenn
Preparation —The ore is mined by pick and shovel, crushed and
washed It is then, in some cases, dried and broken into fine particles
The fine dust is separated from the coarser material, and the latter,
which comprises most of the ore, is heated to 400° This changes the
iron compounds to magnetic oxide which is separated electro-mag-
neticaJly The concentrate contains about 86 per cent of AfaOb This
is then purified and dissolved in a molten flux, in some cases cryolite,
and is subjected to electrolysis The quantity of aluminium made in the
United States during 1912 was over 65,600,000 Ib , valued at about
$17,000,000. The value of the aluminium salts produced was about
$3,000,000.
Uses — Bauxite (or more properly the mixture of bauxite and gibbs-
ite) is practically the only commercial ore of aluminium which, on
account of its lightness and its freedom from tarnish on exposure, has
become a very popular metal for use in various directions It is em-
ployed in castings where light weight is desired and in the manufacture
of ornaments and of plates for interior metallic decorations It is also
employed in the steel industry, and, in the form of wire, for the trans-
mission of electricity The mineral is also used in the manufacture of
aluminium salts, in making alundum (artificial corundum), and bauxite
brick for lining furnaces, and in the manufacture of paints and alloys.
Production — The bauxite mined in the United States during 1912
amounted to about 159,865 tons valued at $768,932, the greater portion
coming from Arkansas This is about two-thirds the value of the pro-
duction of the entire world
Psilomelane
Psilomelane is probably a mixture of colloidal oxides and hydroxides
of manganese in various proportions In most specimens there is a
notable percentage of BaO or £20 present, and m others small quantities
of lithium and thallium. The barium and potassium components are
thought to have been absorbed from their solutions
The substance occurs in globular, botryoidal, stalactitic, and massive
forms exhibiting, in many instances, an obscure fibrous structure Its
color is black or brownish black and its streak brownish black and
glistening. Its hardness is 5 5-6 and specific gravity 4.2
Psilomelane is infusible before the blowpipe, m some cases coloring
the flame green (Ba) and in others violet (K). With fluxes it reacts for
HYDROXIDES 189
manganese. In the closed tube it yields water. It is soluble in HC1
with evolution of chlorine
It is distinguished from most other manganese oxides and hydroxides
by its greater hardness.
Occurrence — Psilomelane occurs in veins associated with pyrolusite
and other manganese compounds, as nodules in clay beds, and as coatings
on many mangamferous minerals In all cases it is probably a product
of weathering
Locahties — It is found in large quantity at Elgersburg in Thuringia;
at Ilfeld, Harz, and at various places in Saxony. In the United States
it occurs with pyrolusite and other ores of manganese at Brandon, Vt ;
in the James River Valley, and the Blue Ridge region of Virginia; in
northeastern Tennessee; at Cartersville, Georgia, at Batesville, Arkan-
sas, and in a stretch of country about forty miles southeast of San
Francisco, California. At many of these points it has been mined as an
ore of manganese
Wad
Wad is a soft, earthy, black or dark brown aggregate of manganese
compounds closely related to psilomelane
It occurs in globular, botryoidal, stalactitic, flaky and porous
masses, which, m some cases, are so light that they float on water. It
also occurs in fairly compact layers and coats the surfaces of cracks,
often forming branching stains, known as dendntes
Wad contains more water than psilomelane, of which it appears
often to be a decomposition product. More frequently it results from
the weathering of manganiferous iron carbonate It is particularly
abundant in the oxidized portions of veins containing manganese car-
bonates and silicates
Wad is easily distinguished from all other soft black minerals, except
pyrolusite^ by the reaction for manganese, and from all other manganese
compounds, except pyrolusite, by its softness From pyrolusite it is
distinguished by its content of water.
Localities— It occurs in most of the localities at which other man-
ganese compounds are found.
DIASPORE GROUP
The diaspore group comprises the hydroxides of aluminium, iron
and manganese, possessing the general formula R'"O(OH). They are
regarded as hydroxides in which one of the hydrogens in BfeO is replaced
by the group R/7/0, thus: H— O— H, water, A10— 0— H, diaspore These
190
DESCRIPTIVE MINERALOGY
three compounds from a chemical viewpoint, may be looked upon as the
acids whose salts comprise the spinel group of minerals, which includes
among others the three important ore minerals magnetite, chromite and
frankhnite Of the three members of the diaspore group the manganese
and iron compounds are valuable ores All are orthorhombic, in the
rhombic bipyramidal class.
Diaspore (AIO(OH))
Diaspore is found in colorless or light colored crystals, in foliated
masses and in stalactitic forms
Its composition is theoretically 85 per cent AbOs and 15 per cent
Fro 92 — Diaspore Crystals oo P So , oio (fi) , oo Pj , 130 (s) , GO P, no (m),
210 (A), PS5, on (e), ?2, 212 (s), ooPl, 120 (/), « P<j, 150 («),
HgO, though analyses show it to contain, in addition, usually, some iron
and silicon A specimen from Pennsylvania yielded.
A1203
8095
H20
14 84
Fe20s
3 12
Si02 Total
i 53 100 44
Other specimens approach the theoretical composition very closely
In crystallization the mineral is orthorhombic (rhombic bipyramidal
class), with a b . c= 9372 . i : 6039 The crystals are usually pris-
matic, though often tabular parallel to oo P 56 (oio) The principal
planes observed on them are oo Poo (oio), a series of prisms as
ooP(no), oo Pa (210), °oP3(i3o), the dome PQ&(OII) and several
pyramids (Fig. 92) The planes of the prismatic zone are often ver-
tically striated The angle no A i Io-86° if
The cleavage of diaspore is very distinct parallel to the brachy-
pmacoid. Its fracture is conchoidal and the mineral is very brittle,
Its hardness is about 6 5 and density 3 4 The luster of the mineral is
vitreous, except on the cleavage surface, where it is pearly. Its color
HYDROXIDES 191
varies widely, though the tint is always light and the streak colorless
The predominant shades are bluish white, grayish white, yellowish or
greenish white The mineral is transparent or translucent It is a
nonconductor of electricity Its refractive indices for yellow light are
a= 1702, j8=i 722, 7 = 1 750
In the closed tube diaspore decrepitates and gives off water at a high
temperature It is infusible and insoluble in acids. When moistened
with a solution of cobalt nitrate and heated it turns blue, as do all other
colorless aluminium compounds
In appearance, diaspore closely resembles Irucite (Mg(OH)s), from
which it may be distinguished by its greater hardness and its aluminium
reaction with cobalt nitrate
Synthesis — Crystal plates of diaspore have been made by heating at
a temperature of less than 500°, an excess of amorphous AfeQs in sodium
hydroxide, enclosed in a steel tube At a higher temperature corundum
resulted.
Occurrence — Diaspore occurs as crystals implanted on corundum
and other minerals, and on the walls of rocks in which corundum is
found It is probably in most cases a decomposition product of other
aluminium compounds
Localities — In Ekaterinburg, Russia, it is associated with emery.
At Schemnitz, Hungary, it occurs in veins It is found also in the
Canton of Tessin, in Switzerland, at various places in Asia Minor, and
on the emery-bearing islands of the Grecian Archipelago. In the
United States it is associated with corundum, at Newlin, Chester Co ,
Penn , with emery at Chester, Mass , at the Culsagee corundum mine,
near Franklin, N C , and at other corundum mines in the same State.
Manganite (MnO(OH))
Manganite usually occurs in groups of black columnar or prismatic
crystals and in stalactites.
The formula MnO(OH) requires 27 3 per cent 0, 62 4 per cent Mn
and 10 3 per cent water, or 89 7 per cent MnO and 10 3 per cent water.
In addition to these constituents, the mineral commonly contains also
some iron, magnesium, calcium and often traces of other metals. An
analysis of a specimen from Langban, in Sweden, yielded:
Mn2O3 Fe203 MgO CaO H2O Total
88 51 23 i 51 62 9 80 100 67
The orthorhombic crystals of the mineral have an axial ratio a : i : c
= 8441 : i : ,5448 The crystals are nearly all columnar with a series
192
DESCRIPTIVE MINERALOGY
of pnsms, among which are oo P^io) and oo P(uo), and the two lateral
pinacoids oo P 06 (oio) and 8 P a (100) terminated by oP(ooi) or by
the domes P 06 (on), P 06 (101), and pyramids (Figs 93 and 94) Cru-
ciform and contact twins, with the twinning plane P oo (on), are not
uncommon (Fig 95) The prismatic surfaces are
vertically striated and the crystals are often in
bundles The angle no A iTo=8o° 20'
Cleavage is well defined parallel to oo P 06 (oio)
and less perfectly developed parallel to ooP(no)
The fracture is uneven The luster of the mineral
is brilliant, almost metallic Its color is iron-black
and its streak reddish brown or nearly black It
is usually opaque but in very thin splinters it is
sometimes brown by transmitted light. Its hard-
ness is 4 and density about 4 3. The mineral is
a nonconductor of electricity
Mangamte yields water in the closed tube and colors the borax bead
amethyst m the oxidizing flame of the blowpipe. In the reducing flame,
upon long-continued heating, this color disappears The mineral dis-
solves in hydrochloric acid with the evolution of chlorine. It is dis-
FIG 93 — Mangamte
Crystal with ooP,
no(w), oP,ooi (c)
and P 55 , ioi («)
FIG 94 — Group of Prismatic Mangamte Crystals from Lfeld, Hare.
tinguished from other manganese minerals by its hardness and crystal-
lization.
By loss of water mangamte passes readily into pyrolusite (MnCfe).
It also readily alters into other manganese compounds
Synthesis.— Upon heating for six months a mixture of manganese
chloride and damn caarbonate fine crystals like those of mangamte
HYDROXIDES 193
have been obtained Their composition, howe\er, was that of haus-
manmte, indicating that \\hile mangamte was produced, it was changed
to hausmanmte during the process.
Occurrence, Localities and Origin — Man-
gamte occurs in veins in old volcanic rocks,
and also in limestone It is found at Ilfeld
in the Harz, at Ilmenau in Thurmgia, and
at Langban in Sweden, in handsome cns-
tals In the United States it occurs at the
Jackson and the Lucie iron mines, Xegaunee,
Mich , and in Douglas Co , Colo It is _
, , , . A : „ FIG 05— Manoamte Crvstal
also abundant at ^arlous places m New Tvvmned abjut P^('QII^
Brunswick and Nova Scotia In all cases The torms are =c P notmj,
it is a residual product of the weathering of =cP3,i2o./;andP3 31315)
manganese compounds.
Uses — Mangamte is used in the production of manganese compounds.
As mined it is usually mixed with pyrolusite, this being the most im-
portant portion of the mixture
Goethite (FeO(OH))
This mineral, though occasional!}- found m blackish brown crystals,
usually occurs in radiated globular and botryoidal masses Analyses
of specimens from Maryland, and from Lostwithiel, in Cornwall, gave-
Fe20s Mn2Q3 H2O SiCb Total
Maryland 86 32 10 So 2 88 too oo
Lostwithiel 89 55 16 10 07 28 100 06
The formula FeO(OH) demands 89.9 per cent Fe2Qs and 10 i per cent
H2O or 62.9 per cent Fe, 27 o per cent 0 and 10 i per cent HaO
Like diaspore and mangamte, goethite is orthorhornbic, its axial
ratio being a : b : c = 9185 : i : .6068 Its crystals are prismatic or
acicular with the prisms plainly striated vertically The forms observed
are commonly oo P 06 (oio), QO PS(2io\ oo P(no), P 06 (on) and P(rii).
The angle no A 1*10=85° 8'.
The deavage of goethite is perfect parallel to oo P 06 (oio) and its
fracture uneven Its hardness is 5 and density about 4.4. Its color is
usually yellowish, reddish or blackish brown and its luster almost
metallic In thin splinters it is often translucent with a blood-red color
and a refractive index of about 2 5 Its streak is brownish yellow. It
is an electric nonconductor.
194 DESCRIPTIVE MINERALOGY
The chemical reactions of the mineral are about the same as those of
hematite, except that it yields water when heated in the closed tube
By this reaction it is easily distinguished from the fibrous varieties of
hematite, as it is also by its streak
Synthesis — Needles of goethite are produced by heating freshly
precipitated iron hydroxide for a long time at 100°
Occurrence and Localities — Goethite is usually associated with other
ores of iron, especially in the upper portion of veins, -where it is produced
by weathering. It is found near Siegen in Nassau, near Bristol and
Clifton, England, and in large, fine crystals at Lostwithiel and other
places in Cornwall
In the United States it occurs in small quantity at the Jackson and
the Lucie hematite mines in Negaunee, Mich , at Salisbury, Conn ,
at Easton, Penn , and at many other places
Uses — Goethite is used as an ore of iron, but in the trade it is classed
with limomte as brown hematite
CHAPTER DC
THE ALU3IIXATES, FERRITES, CHROMITES \XD MAXG \XITES
MOST of these compounds are salts of the comparative!} uncommon
acids HA1O2, HFeOo and HCrCb, \\hich may be regarded as metaacids
derived from the corresponding normal acids by the abstraction of water,
thus. HsAlOs— H2O=HAlOo There are onh a few minerals belong-
ing to the group but they are important One, magnetite, is an ore of
iron, another, chronute, is the principal ore of chromium and two others
are utilized as gems Most of them are included in the mineral group
known as the spmels (Compare p 189 )
That there is a manganese acid corresponding to the metaacids of AI,
Fe and Cr is indicated by the fact that in some of the spinels manganese
replaces some of the fernc iron, as, for example, in frankhmte. This
suggests that this mineral is an isomorphous mixture of a metafernte
and a salt of the corresponding manganese acid (HMnCb) This may
be regarded as derived from the hydroxide, MnfOH)s, by abstraction
of H2O, thus- H3Mn03-H2CMHMnO.>. But there are other man-
ganous acids Normal manganous acid is MnfOH)^, or H4Mn(>4 If
from this one molecule of water be abstracted, there remains H2^InOs,
the metamanganous acid The manganous salt of the normal acid,
Mn2MnQi, occurs as the mineral, hausmannite, and the corresponding
salt of the metaacid, MnMnOs, as the mineral, braunite.
SPINEL GROUP
The spinels are a group of isomorphous compounds that may be
regarded as salts of the acids AIO(OH), MnO(OH), CrO(OH) and
FeO(OH), in which the hydrogen is replaced by Mg, Fe and Cr.
Al— 0— CX
Thus, spinel, Mg- AfeQ* may be regarded as || yMg, magnetite,
Fe— 0— Ov Cr— O-Ov
Fe3O4, as II >Fe; clromite, FeCx&O*, as || )>Fe, and
Fe-O-(X Cr-O-CK
(Fe Mn)-O-<X
frankhmte, as I I y>(Zn-Mn Fe). Chemical compounds of
(Fe Mn)-0-CK
195
196
DESCRIPTIVE MINERALOGY
this general type are fairly numerous, but only a few occur as minerals
The most important are the three important ores mentioned above,
spinel is of some value as a gem btone
The spinels crystallize in the holohedral divi-
sion of the isometric system (hexoctahedral class),
in well defined crystals that are usually combina-
tions of 0(ui) and ooO(no), with the addition on
some of ooQoo (100), 303(311), 202(211), 50^(531),
etc Contact twins are so common with 0 the
twinning plane, that this type of twinning is often
referred to as the spinel twinning (Fig 96).
FIG 96
Spinel Twin
The complete list of the known spinels is as follows.
Spinel
Ceylomte (pleonaste)
CJdorspinel
Picotite
Hercynite
Gahmte
Dysluite
Krwttomte
Magnetite
Magnesiofernte
Frankhmte
Jacobsite
Chromite
Mg(A102)2
(Mg Fe)(A102)2
Mg((Al Fe)02)2
(Mg Fe)((Al Fe-Cr)02)2
Fe(A102)2
Zn(A102)2
(Zn Fe Mn)((Al Fe)02)2
(Zn Fe Mg) ((Al Fe)O2)2
Fe(Fe02)2
Mg(Fe02)2
(Fe ZnMn)((Fe Mn)O2)2
(Mn Mg)((Fe Mn)02)2
(Fe Mg)(Cr Fe)02)2
Spinel (Mg(AlO2)2)
Ordinary spinel is the magnesian alummate, which, when pure, con-
tains 28 3 per cent MgO and 71 7 per cent
AfeOa Usually, however, there are present
admixtures of the other isomorphs so that
analyses often indicate Fe, Al and Cr
The mineral usually occurs in isolated
simple crystals, rarely in groups The forms
observed on them are 0(m), ooO(no) and
303(311), and rarely oo 0 oo (100) (Fig 97)
The pure magnesium spinel is colorless or FlG 97— Spinel Crystal
some shade of pink or red, brown or blue, and J^'Q (^r£)"°
is usually transparent or translucent, though an 3 3' 3I1
opaque varieties are not rare Its streak is white It possesses a glassy
ALUMINATES, FERRITES, ETC 197
luster, and a conchoidal fracture, but no distinct cleavage Its hard-
ness is 8 and its density 3 5-3 6 Its refractive indices \ary with the
color n for yellow light is i 7150 for red spinel and i 7201 for the blue
variety.
The mineral is infusible before the blowpipe and is unattacked by
acids It yields the test for magnesia with cobalt solution
Spinel is easily distinguished from most other minerals by its cns-
tallization and hardness It is distinguished from pale-colored garnet
by its blowpipe reactions, especially its infusibility, and its failure to
respond to the test for Si02
The best known varieties are:
Precious spinel, which is the pure magnesian aluminate. It is trans-
parent and colorless or some light shade of red, blue or green. The
bright red variety is known as ruby spinel and is used as a gem Its
color is believed to be due to the presence of chromium oxide It is
easily distinguished from genuine ruby by the fact that it is not doubly
refracting and not pleochroic.
The best ruby spinels come from Ceylon, where they occur loose in
sand associated with zircon, sapphire, garnet, etc.
Common spinel differs from precious spinel m that it is translucent.
It usually contains traces of iron and alumina.
Both these varieties of spinel occur in metamorphosed limestones
and crystalline schists.
Syntheses — The spinels have been made by heating a mixture of
AkOs and MgO with boracic acid until fusion ensues, and by heating
Mg(OH)2 with AlCls in the presence of water vapor
Origin — Spinel has been described as an alteration product of corun-
dum and garnet It is also a primary component of igneous rocks and
a product of metamorphism in rocks nch in magnesium
Uses — Only the transparent ruby spinels have found a use. These
are employed as gems
Ceylonite, or pleonaste, is a spinel in which a portion of the Mg
has been replaced by Fe, i e , is an isomorphous mixture of the magne-
sian and iron aluminates, thus ((Mg Fe)(AlO2)2) It is usually black
or green and translucent, and has a brownish or dark greenish streak
and a density =3 5-3 6
The analysis of a sample separated from an igneous rock in Madison
Co , Mont., gave,
A12O3 FeO MgO CraOs Fe^ MnO CaO SiOa Total
62 09 17 56 15 61 2 62 2 10 tr 16 55 100 69
198 DESCRIPTIVE MINERALOGY
Ceylomte occurs in igneous rocks m the Lake Laach region,
Germany, and m the Piedmont district, Italy and elsewhere, m meta-
morphosed limestones at Warwick and Amity, N Y , m the limestone
blocks enclosed in the lava of Vesuvius, and m dolomite metamor-
phosed by contact action at Monzoni, Tyrol
Picotite, or chrome spinel, is a \anety intermediate between spinel
proper and chromite Its composition may be represented by the
formula (Mg Fe)((Al Fe Cr)O2)2 It occurs only m small crystals in
basic igneous rocks and in a few crystalline schists Density =4 i
Magnetite (Fe(FeO2)2)
Magnetite, the ferrous fernte, the empirical formula of which is
FesO-i, is a heavy, black, magnetic mineral which is utilized as one of
the ores of iron
The pure mineral consists of 72 4 per cent Fe and 27 6 per cent 0
Most specimens, however, contain also some Mg and many contain small
quantities of Mn or Ti A selected sample of magnetite from the Eliza-
beth Mine, Mt Hope, New Jersey, analyzed as follows
Fe2O3 FeO Si02 Ti02 A1203 MgO CaO Other Total
65 26 30 20 i 38 i 09 55 10 68 73 99 99
Magnetite occurs in crystals that are usually octahedrons or dodeca-
hedrons, or combinations of the two , Other forms are rare Twins
are common The mineral occurs also as sand
and in granular and structureless masses When
the dodecahedron is present, its faces are fre-
quently striated parallel to the edge between
ooO(no) and 0(ui) (Fig 98)
Magnetite is black and opaque and its streak FIG 98 —Magnetite
is black It has an uneven or a conchoidal f rac- Crystal, with w o
ture, but no distinct cleavage Its hardness is (llo) and ° (l3CI)»
S.S^anddeM1ty49-5* It is strongly attracted f™*
by a magnet and in many instances it exhibics and in
polar magnetism
The mineral is infusible before the blowpipe Its powder dissolves
slowly in HC1, and the solution reacts for ferrous and ferric iron
Magnetite is easily recognized by its color, magnetism, and hardness
The mineral weathers to lunomte and hematite and occasionally to
the carbonate, sidente,
ALUMINATES, FERRITES, ETC. 199
Syntheses. — Crystals have been made by cooling iron-bearing silicate
solutions, treating heated ferric hydroxide \\ith HC1, and by fusing
iron oxide and borax with a reducing flame
Occurrence end Ongm. — The mineral occurs as a constituent of
many igneous rocks and crystalline schists, and in lenses embedded in
rocks of many kinds It also constitutes veins cutting these rocks
and as irregular masses produced b\ the deh\ dration and deoxidation
of hematite and limomte under the influence of metamorphic processes.
It occurs also as little grains among the decomposition products of
iron-bearing silicates, such as olmne and hornblende.
The larger masses are either segregations from igneous magmas or
deposits from hot solutions and gases emanating from them.
Localities — The localities at \\hich magnetite has been found are so
numerous that only those of the greatest economic importance may be
mentioned here. In Norway and Sweden great segregated deposits are
\\orked as the principal sources of iron in these countries. In the
United States large lenses occur in the limestones and siliceous crys-
talline schists in the Adirondacks, New York, and in the schists and
granitic rocks of the Highlands in New Jersey Great bodies are mined
also at Cornwall, and smaller bodies at Cranberry, and in the Far
West
Extraction — The magnetite is separated from the rock with which it
occurs by crushing and exposing to the action of an electro-magnet.
Production — The total amount of the mineral mined m the United
States during 1912 was 2,179,500 tons, of which 1,110,345 tons came
from New York, 476,153 tons from Pennsylvania, and 364,673 tons
from New Jersey.
FrankEnite ((Fe-Zn Ua)((Fe-Hn)O2)2)
Franklinite resembles magnetite in its general appearance. It is an
ore of manganese and zinc
It differs from magnetite m containing Mn in place of some of the
ferric iron in this mineral and Mn and Zn in place of some of its ferrous
iron. Since it is an isomorphous mixture of the iron, zinc and manganese
salts of the iron and manganese acids of the general formula R"'0(OH),
its composition varies within wide limits The franklinite from Mine
Hill, N. J , contains from 39 per cent to 47 per cent Fe, 10 per cent to
19 per cent Mn and 6 per cent to 18 per cent Zn A specimen from
Franklin Furnace, N J., contained,
Fe203 MnO ZnO MgO CaO SiOa HsO Total
66 58 9 96 so 77 34 -43 -72 -71 99-5*
200 DESCRIPTIVE MINERALOGY
Its crystals are usually octahedrons, sometimes modified by the do-
decahedron and occasionally by other forms The mineral occurs also
in rounded grams, in granular and in structureless masses
It is black and lustrous and has a dark brown streak Its fracture
and cleavage are the same as for magnetite It is only very slightly
magnetic It has a hardness of 6 and a density of 5 15
The mineral is infusible before the blowpipe When heated on
charcoal it becomes magnetic When fused with Na2COa in the oxidizing
flame it gives the bluish green bead characteristic of manganese Its
fine powder mixed with Na2COa and heated on charcoal yields the white
coating of zinc oxide which turns green when moistened with Co(N03)2
solution and again heated
Franklinite is distinguished from most minerals by its color and crys-
tallization and from magnetite and clromite by its brown streak and
by its reactions for Mn and Zn It is also characterized by its associa-
tion with red zmcite and green or pink willemite (p 306)
Synthesis — Crystals of franklmite have been made by heating a
mixture of FeCla, ZnCb and CaO (lime)
Occurrence and Origin — Franklimte occurs at only a few places Its
most noted localities are Franklin Furnace and Sterling Hill, N J , where
it is associated in a white crystalline limestone with zmcite, willemite
and other zinc and manganese compounds The deposit is supposed
to have been produced by the replacement of the limestone through the
action of magmatic waters and vapors.
Uses. — The mineral is utilized as an ore of manganese and zinc
The ore as mined is crushed and separated into parts, one of which
consists largely of franklmite This is roasted with coal, when the zinc
is driven off as zinc oxide The residue is smelted in a furnace producing
spiegeleisen, which is an alloy of iron and manganese used in the man-
ufacture of certain grades of steel
Production — The quantity of this residuum produced in 1912 was
104,670 tons, valued at $314,010
Chromite (Fe(CrO2)2)
Chromite, or chrome-iron, is the principal ore of chromium. It
resembles magnetite and frankhnite in appearance It occurs in iso-
lated crystals, in granular aggregates, and in structureless masses.
Chemically, it is a ferrous salt of metachromous acid, of the theoret-
ical composition Cr20a=68 per cent and FeO=32 per cent, but it usually
contains also small quantities of Al^Oa, CaO and MgO An analysis of
ALUMINATES, FERRITES, ETC 201
a specimen from Chorro Creek, California, after making corrections for
the presence of some serpentine, yielded
Cr203 A1203 Fe203 FeO MgO MnO Total
56 96 12 32 3 81 12 73 14 02 16 100 oo
Its crystals are usually simple octahedrons, but they are not as
common as those of the other spinels
Its color is brownish black and its streak brown It has a conchoidal
or uneven fracture and no distinct clea\age It is usually nonmag-
netic, but some specimens sho\\ slight magnetism because of the ad-
mixture of the isomorphous magnetite molecule Its hardness is 5 5
and its density 4 5 to 4 8
The mineral is infusible before the blowpipe It gives the chromium
reaction with the beads If its powder is fused with niter and the fusion
treated with water, a yellow solution of KoCrO4 results When fused
with NagCOs on charcoal it yields a magnetic residue.
Chromite is easily distinguished from all other minerals but ptco-
tite by its crystallization and its reaction for chromium. It is distin-
guished from picotite by its inferior hardness and its higher specific
gravity.
Synthesis — Crystals have been made by fusing the proper constit-
uents with boric acid and after fusion distilling off the boric acid.
Occurrence and Origin — Chromite occurs principally in olivine rocks
and in their alteration product — serpentine The mineral is found not
only as crystals embedded in the rock mass, but also as nodules in it
and as veins traversing it It is probably in all cases a segregation from
the magma producing the rock In a few places the mineral occurs
in the form of sand on beaches
Localities — It is widely spread through serpentine rocks at many
places, notably in Brussa, Asia Minor; at Banat and elsewhere in
Norway; at Solnkive, in Rhodesia, in the northern portion of New
Caledonia, at various points in Macedonia, in the Urals, Russia; in
Beluchistan and Mysore, India
In the United States the mineral is known at several points in a belt
of serpentine on the east side of the Appalachian Mountains, and at
many points in the Rocky Mountains, the Sierra Nevada and the Coast
Ranges It has been mined at Bare Hills, Maryland, in Siskiyou,
Tehama and Shasta Counties, Colorado, in Converse County, Wyoming;
and in Chester and Delaware Counties, Pennsylvania, and in 1914,
some was washed from chrome sand at Baltimore, Maryland.
202 DESCRIPTIVE MINERALOGY
Metallurgy —The mineral is mined by the usual methods and con-
centrated, or, if in large fragments, is crushed It is then fused with
certain oxidizing chemicals and the soluble chromates are produced.
Or the ore is reduced with carbon yielding an alloy with iron The
metal is produced by reduction of its oxide by metallic aluminium or by
electrolysis of its salts
jjses — Chromite is the sole source of the metal chromium, which is
the chrome-iron alloy employed m the manufacture of special grades
of steel Chromium salts are used in tanning and as pigments The
crude ore, mixed with coal-tar, kaolin, bauxite, or some other ingredient,
is molded into bricks and burned, after which the bricks are used as
linings in metallurgical furnaces. These bricks stand rapid changes of
temperature and are not attacked by molten metals
Production — The annual production of chromite in the world is
now about 100,000 tons, of which Rhodesia produces about J, New
Caledonia about | and Russia and Turkey about \ each The produc-
tion of the United States in 1912 was 201 tons, valued at $2,753. All
came from California. The imports in the same year were 53,929 tons,
worth $499,818.
Chiysoberyl
Chrysoberyl is a beryllium alummate, the composition of which is
analogous to that of the spinels It may be written Be02(A10)2. Al-
though theoretically it should contain 19 8 per cent BeO and 80 2 per
cent AkOa, analyses of nearly all specimens show the presence also of
iron and magnesium
The mineral differs from spinel in crystallizing in the orthorhombic
system (bipyramidal class) Its axial ratio is .4707 : i : 5823 The
principal forms observed on crystals are P(in), ooP 06(100),
oo P oo (oio), P 06 (on), oo P2(i2o) and 2P?(i2i) (Fig 99) The crystals
are often twins (Fig 100), trillings or sixlmgs, with 3? 06 (031) the
twinning plane, forming pseudohexagonal groupings (Fig 101) Sim-
ple crystals are usually tabular parallel to oo P So (100), which is striated
vertically Consequently, in twins this face exhibits stnations arranged
feather-like. The angle no A iTo=5o° 21'.
The deavage of chrysoberyl is distinct parallel to Poo (on), and
indistinct parallel to oo P 06 (oio) and oo P 56 (100) Its fracture is
uneven or conchoidal. Its color is some shade of light green or yellow
by reflected light. It is transparent or translucent and in some cases is
distinctly red by transmitted light. It is strongly pleochroic m orange,
ALUMINATES, FERRITES, ETC
203
green and red tints. The mineral is brittle, has a hardness of 8 5 and a
density of about 3 6 Its refractive indices are a=i 7470, j5=i 7484,
Four distinct varieties are recognized
Ordinary, pale green, translucent
Gem, yellow and transparent
Alexandrite, emerald-green in color, but red by transmitted light,
transparent, usually in twins Used as a gem
Cat's-eye, a greenish variety exhibiting a play of colors (chatoyancy )
Before the blowpipe the mineral is infusible It yields the Al reac-
tion with Co(NOs)2, but otherwise is only slightly affected by the flame
It is insoluble in acids
Chrysoberyl is characterized by its crystallization and great hard-
FIG 99
FIG ioo
FIG 101
FIG 99 — Chrysoberyl Crystal with oo P GO 3 100 (a), oo P 55 , oio (b), oo P7, 120 (s),
2&2t 121 («), P, in (o) and P oo , on (i).
FIG 100 — Chrysoberjl Thinned about 3? So (031)
FIG 1 01 — Chrysobeiyl Pseudohexagonal Sixlmg Twinned about 3? 5 (031)
ness It most closely resembles the beryllium silicate, beryt, in appear-
ance, but is easily distinguished from this by its crystallization.
Synthesis. — Crystals have been made by fusing BeO and AkOs
with boric acid and then distilling off the boric acid
Occurrence and Origin — Chrysoberyl is found principally in granites
and crystalline schists and as grains in the sands produced by the erosion
of these rocks In its original position the mineral is a separation
from the magma that produced the rocks.
Localities. — Its best known localities are in Minas Geraes, Brazil,
near Ekaterinburg, Ural; in the Mourne Mts,, Ireland, at Haddam,
Conn , at Greenfield, N. Y.; at Orange Summit, N. Hamp.; and at
Norway and Stoneham, Me. The alexandrite comes from Ceylon, where
it occurs as pebbles, and from the Urals.
204
DESCRIPTIVE MINERALOGY
Braunite (MnMnOs) occurs massive and in crystals. The latter
are tetragonal (ditetragonal bipyramidal class), 'with a c—i 9922,
They are usually simple bipyramids P(in) Because of the nearly
equal value of a and c all crystals are isometric in habit The angle
iiiAii"i 70° 7' Twins are common, with POO(IOI) the twinning
plane Cleavage is perfect parallel to P(III)
The mineral is brownish black to steel-gray m color and in streak
Its luster is submetallic Its hardness is 6-6 5 and density 47 It is
infusible before the blowpipe With fluxes it gives the usual reactions
for manganese It is soluble in HC1 yielding chlorine
It occurs in veins with manganese and other ores in Piedmont, Italy,
and at Pajsberg and various other places m Sweden, where its origin
is secondary
Hausmannite (MngMnO^ crystallizes like braumte, but a : <:=
i : 1 1573 and its crystals are, therefore, distinctly tetragonal m habit
They are usually simply P(ni) or combinations of P(m) and fP(ii3),
though much more complicated crystals are known The angle
niAi7i=6o° i' Twins and fourlmgs (Fig 102) are common, with
FIG 102 —Hausmannite. (A) Simple Crystal, P, in (p) and oP, ooi (c) (B)
Fivelmg Twinned about P oo (101)
P oo (101) the twinning plane The cleavage is imperfect parallel to
oP(ooi) The mineral also occurs in granular masses.
Hausmannite is brownish black Its streak is chestnut brown
Its hardness is 5-5 5 and density 4 8. Its reactions are the same as
those of braumte
Hausmannite occurs as crystals at Ilmenau, Thurmgia, Ilfdd,
Harz, and as granular masses in dolomite at Nordmark and several
other points in Sweden Like braumte it is probably a decomposition
product of other manganese minerals
CHAPTER X
THE NITRATES AND BORATES
THE OTTBATES
THE nitrates are salts of nitric acid Only two are of importance
to us, saltpeter (KNOa) and chile saltpeter (NaNOs) Both are color-
less, or white, crystalline bodies, both are soluble m water and both pro-
duce a cooling taste when applied to the tongue The potassium com-
pound is distinguished from the sodium compound by the flame test
Both minerals when heated in the closed tube with KHSOi yield red
vapors of nitrogen peroxide (NCfe)
Soda Niter (NaNO3)
Soda niter, or chile saltpeter, is usually m incrustations on mineral
surfaces or m massi\ e forms It consists of 63 5 per cent N2Os and
36 5 per cent Na20
Its crystals are in the ditrigonal scalenohedral class of the hexagonal
system with an axial ratio of a : c=i : 8297. They are usually rhom-
bohedrous R(ioTi) m some cases modified by oR(oooi). Apparently
the mineral is completely isomorphous with calcite (CaCOs)
Its cleavage is perfect parallel to the rhombohedron. Its hardness
is under 2, its density about 2.27 and its melting point about 312°.
Its luster is vitreous, color white, or brown, gray or yellow. The min-
eral is transparent Its refractive indices for yellow light are: w = 1.5854,
€=13369
Soda niter deflagrates when heated on charcoal and colors the flame
yellow. When exposed to the air it attracts moisture and finally lique-
fies. It is completely soluble in three times its own weight of water.
Occurrence and Localities — The principal occurrences of the mineral
are in the district of Tarapaca, northern Chile, where, mixed
with the lodate and other salts of sodium and potassium, under the
name caliche, it comprises beds several feet thick on the surface of rain-
less pampas, and in Bolivia at Arane under the same conditions. It is
associated with gypsum, salt and other soluble minerals. Smaller
205
206 DESCRIPTIVE MINERALOGY
deposits are found in Humboldt Co , Nevada, m San Bernardino Co ,
Cal , and in southern New Mexico
The material is thought to result from the action of microorganisms
upon organic matter decomposing in the presence of abundant air
Uses —Soda niter is used in the production of nitric acid, and in the
manufacture of fertilizers and gunpowder About 480,000 tons are
imported into the United States annually at a cost of $15,430,000
Most of it comes from Chile
Since soda niter usually contains sodium lodate as an impurity, the
mineral is an important source of iodine.
Niter (KNO3)
Niter, or saltpeter, resembles soda niter in appearance It gener-
ally occurs in crusts, in silky tufts and in groups of acicular crystals
Its crystals are orthorhombic with a b : c= 5910 * i 7011 Their
habit is hexagonal The principal forms observed on them are oo P(i 10),
oo P 00(100^, oo P 06(010), oP(ooi), P(in), and a series of brachy-
domes In many respects the mineral is apparently isomorphous with
aragonite which is the orthorhombic dimorph of calcite At 126° it
passes over into an hexagonal (trigonal) form Its cleavage is perfect
parallel to Poo (on) Its fracture is uneven, its hardness 2 and den-
sity 2 i Its medium refractive index for yellow light, /3=i 5056
Niter deflagrates more violently than soda niter and detonates with
combustible substances It fuses at aboat 335° It colors the blowpipe
flaine violet It is soluble in water
Occurrence and Localities — The mineral forms abundantly in dry
soils in Spain, Egypt, Persia, Ceylon and India, where it is produced
by a ferment, and on the bottoms of caves m the limestones of Madison
Co , Ky , of Tennessee, of the valley of Virginia and of the Mississippi
Valley
Production — Most of the niter used in the arts is manufactured, but
some is obtained from the deposits m Ceylon and m India The
amount imported in 1912 aggregated 6,976,000 Ib , valued at $226,851
THE BORAXES
The borates are salts of bone acid, HsBOs, metaboric acid, HBQz,
tetrabonc acid, EfeBiOr, hexabonc acid, EUBoOn, and various poly-
boric acids in which boron is present in still larger proportion The
metaacid is obtained from the orthoacid by heating at 100°, at which
NITRATES AND BORATES 207
temperature the former loses one molecule of water, thus. H3BO3 —
H2O=HBO2, and the tetraacid by heating the ^ame compound to 160"
at which temperature 5 molecules of \\ater are lost from 4 molecules ot
the acid, thus 4H3B03-5H2O=H2B407 Hexabonc acid may be
regarded as the orthoacid less i| molecules of water, thus.
Only three of the borates are important enough to be discussed
here These are borax, a sodium tetraborate (NaoB^Or ioH<zO), cole-
manite, a hexaborate (CasBoOn slfeO) and boracite, a magnesium
chloro-polyborate (Mg5(MgCl)2Bi6Q3o)- Borax and colemamte are
commercial substances that are produced in large quantities
All borates and many other compounds containing boron when
pulverized and moistened with HoSO4 impart an intense yellow-green
color to the flame If boron compounds are dissolved in hydrochloric
acid, the solution will turn turmeric paper reddish brown after drying
at 100° The color changes to black when the stain is treated with
ammonia.
Borax (H"a2B4O7 roH2O)
Borax occurs as crystals and as a crystalline cement between sand
grains around salt lakes, as an incrustation on the surfaces of marshes
and on the sands in desert regions, and dissolved
in the water of certain lakes in deserts. It
occurs also as bedded deposits mterlayered with
sedimentary rocks
The composition of borax is 16 2 per cent
Na20, 36 6 per cent B2Qs and 47 2 per cent H^.
Crystals are monoclmic (prismatic class), with
a : b : c=i 0995 : J : -5^29» and 0=73° 25' FlG I03 —Borax Crystal
They are prismatic in habit and in general form with « P, no (m),
resemble very closely crystals of pyroxene. «P5o,iQo (<*),<»?&,
The principal planes occurring on them are °IO_(6)' °^I°°I !f)'
co P 55 (100), oo P(no), oP(ooi), -P(in) and Jj IZI (a) "* 2p' 221
-2P(22i) (Fig. 103). Their cleavage is perfect
parallel to ooP 60(100), and their fracture concfaoidal. The angle
noAiTo=93°.
The mineral has a white, grayish or bluish color and a white streak.
It is brittle, vitreous, resinous or earthy; is translucent or opaque; has
a hardness of 2-2.5, a density of 1.69-1.72, and a sweetish alkaline taste.
On exposure to the air the mineral loses water and tends to become white
208 DESCRIPTIVE MINERALOGY
and opaque, whatever its color in the fresh condition Its medium
refractive index for yellow light, 0= i 4686
Before the blowpipe borax puffs up and fuses to a transparent
globule Fused with fluonte and potassium bisulphate it colors
the flame green It is soluble in water, yielding a weakly alkaline
solution
Occurrence —The principal method of occurrence of the mineral is
as a deposit from salt lakes in and regions, and as incrustations on the
surfaces of alkaline marshes overlying buried borax deposits The
original beds were deposited by the evaporation to dryness of ancient
salt lakes, and the incrustations were produced by the solution of these
deposits by ground water, and the nse of the solutions to the surface by
capillarity.
Localities.— Borax occurs in the water of salt lakes in Tibet, of
several small lakes in Lake County, and of Borax Lake in San Bernardino
County in California, and in the mud and marshes around their borders
It occurs also in the sands of Death Valley in the same State, and in
various marshes in Esmeralda County, Nevada Other large deposits
are found in Chile and Peru
Uses — Borax is used as an antiseptic, in medicine, in the arts for
soldering brass and welding metals, and in the manufacture of cosmetics
Bone acid obtained from borax and colemamte is employed in the
manufacture of colored glazes, in making enamels and glass, as an
antiseptic and a preservative Some of the borates are used as pig-
ments.
Production — Borax was formerly obtained in the United States,
especially in California, Oregon and Nevada, by the evaporation of
the water of borax lakes, by washing the crystals from the mud on their
bottoms and by the leaching of the mineral from marsh soil At pres-
ent, however, nearly all the borax of commerce is manufactured from
colemanite.
Colemanite (Ca2B6On sH2O)
Colemamte occurs in crystals and in granular and compact masses
It is the source of all the borax now manufactured in the United States.
The formula ascribed to the mineral corresponds to 27 2 per cent
CaO, 50.9 per cent 6203 and 21 9 per cent H20. As usually found,
however, it contains a httle MgO and SiCfe. A crystal from Death
Valley, California, yielded:
6203=5070; 0*0=27.31, MgO= 10,
NITRATES AND BORATES
209
\1/
The mineral crystallizes in the monoclmic system (prismatic class),
m short, prismatic crystals (Fig 104), with the axial constants a:b:c
= 7769 . i : 5416 and 0=69° 43', The crystals are usualh rich in
forms Their cleavage is perfect parallel to ocOScloio), and less
perfect parallel to oP(ooi) Their fracture is uneven The angle
no A 110=72° 4'
Colemanite is colorless, milky white, yellowish white or gray It
is transparent or translucent, has a vitreous or adamantine luster, a
hardness of 4 to 4 5 and a specific
gravity of 2 4 Its index of refrac-
tion for yellow light, 18=1.5920
Before the blowpipe it decrep-
itates, exfoliates, and partially
fuses, at the same time coloring
the flame yellowish green. It is
soluble in hot HC1, but from the
solution upon cooling a volumi-
nous mass of boric acid separates
as a white gelatinous precipitate
It is easily distinguished from
other white translucent minerals,
except those containing boron,
by the flame test It is distin-
guished from borax by its insolu-
bility in water and from boracite by its inferior hardness and crystal-
lization
Syntheses — Colemanite has been prepared by treating ulexite
(NaCaBsOe 8H20) with a saturated solution of NaCl at 70°.
Occurrence and Origin — The mineral occurs as indefinite layers
interstratified with shale and limestones that are associated with basalt
The rocks contain layers and nodules of colemanite Gypsum is often
associated with the borate and m some places is in excess. The cole-
manite is believed to be the result of the action of emanations from
the basalt upon the limestone.
Localities — Colemanite occurs in Death Valley, California, near
Daggett, San Bernardino County, and near Lang Station, Los Angeles
County, and at other points in the same State, and in western Nevada,
near Death Valley A snow-white, chalky variety (priceite) has been
found hi Curry County, Oregon, and a compact nodular variety (pander-
mite) at the Sea of Marmora, and at various points in Asia Minor.
Preparation — Colemanite is at the present time the principal source
FIG 104— Colemanite Crystals with =cP
no(m), 3? 5, 301 (v), =*P5c, 100 (a),
* P» , oro (b); oP, ooi fc), -P, in
(£), 2P* 02M«), P3b,ouOO, «pa,
210 U), aPoo, 201 (A), 2P, 221 (u) and
P, In 00
210 DESCRIPTIVE MINERALOGY
of borax The crude material as mined contains from 5 per cent to 35
per cent of anhydrous boric acid (6203) This is crushed and roasted
The colemamte breaks into a white powder vhich is separated from
pieces of rock and other impurities by screening, and then is bagged and
shipped to the refineries where it is manufactured into borax and boracic
acid
Production — The principal mines producing the mineral in 1912
were situated in the Death Valley section of Inyo County, near Lang
Station in Los Angeles County, California, and in Ventura County in
the same State The total production during the year was 42,315
tons of crude ore, valued at $1,127,813 The imports of crude ore,
refined borax and boric acid during the same year were valued at $i 1,200
The production of the United States m boron acid compounds is
about half that of the entire world, with Chile producing nearly all
the rest
Boracite (Mg5(MgCl)2Bi6O3o)
Boracite is interesting as a mineral, the form and internal structure
of which do not correspond, that is, do not possess the same symmetry
Its crystals have the well marked hextetrahedral symmetry of the iso-
metric system, but their internal structure, as revealed by their optical
properties is orthorhombic This is due to the fact that the substance
is dimorphous Above 265° it is isometric and below that temperature
orthorhombic Crystals formed at temperatures above 265° assume
the isometnc shapes. As the temperature falls the substance changes
to its orthorhombic form, and there results a pseudomorph of ortho-
rhombic boracite after its isometric dimorph
It is a salt of the acid which may be regarded as related to boric
acid as follows. SHsBOs— 9H20=H6BsOi5. Ten atoms of hydrogen
in two molecules of the acid are replaced by Mgs and the other two by
a(MgCl). The resulting combination is 31 4 per cent MgO, 7 9 per
cent Cl and 625 per cent BgC^ioi 8(0-Cl=i 9) The mineral
alters slowly, taking up water, so that some specimens yield water on
analysis and in the dosed tube (stassfurti e and parasite).
The forms usually found on the crystals are -(in), ooO(no),
ooOoo(icx>),--(iIi) (Fig. 105). Usually the positive and negative
tetrahedrons may be distinguished by their luster, the faces of the posi-
tive form being brilliant and those of the negative form dull. The
crystals are isolated, or embedded, and rarely in groups They are
NITRATES AND BORATES 211
strongly pyroelectnc with the analogue pole in the negative tetrahedrons.
The mineral is also found massive
Boracite is transparent or translucent and is gra\ , yellow, or green
Its streak is white Its luster is vitreous Its cleavage is indistinct
parallel to 0(m) and its fracture is conchoidal ^ n ^
The mineral is brittle Its hardness is 7 and
its density 3 Its refractive index £, for yellow
light, = i 667
Boracite fuses easily before the blowpipe
with intumescence to a white pearly mass, at
the same time colonng the flame green With
copper oxides it colors the flame azure-blue FIG 105 —Boracite
When moistened with Co(NOs)2 it gives the Cr>stal with =cO=c,
pink reaction for magnesium Some massive «»/iz;, «O, no id),
forms yield water in the closed tube, in conse- -\ — , m (0) and — ~f
quence of weathering The mineral is soluble _ , ,
inHCl ll
Boracite is distinguished from other boron salts by its crystallization,
its lack of cleavage and its much greater hardness The massive vari-
eties which resemble fine-grained white marble can be distinguished
from this by the flame coloration, hardness and reaction with HC1
Syntheses. — Crystals have been formed by heating borax, MgCfe
and a little water at 275°, and by fusing borax with a mixture of NaCl
and MgCk
Occurrence. — Boracite occurs in beds with anhydrite, gypsum and
saltj and as crystals in metamorphosed limestones
Localities — It is found as crystals in gypsum and anhydrite at
Luneburg, Hanover, and Segeberg, Holstein, in carnallite at Stassfurt,
Prussia, and in radiating nodules (stassfurtite) and in massive layers
associated with salt beds at the last-named locality It is rare in the
United States
Uses and Prodwhon —Boraute is utilized in Europe as a source of
boron compounds. Turkey produces annually about 12,000 tons,
CHAPTER XI
THE CARBONATES
THE carbonates constitute an important, though not a very large,
group of minerals, though one of them, calcite, is among the most com-
mon of all minerals They are all salts of carbonic acid (EkCOs) Those
in which all the hydrogen has been replaced by metal are normal salts,
those in which the replacement has been by a metal and a hydroxyl
group are basic salts Both groups are represented by common minerals
The normal salts include both anhydrous salts and salts combined
with water of crystallization Illustrations of the three classes of car-
bonates are- CaCOs, calcite, normal salt, Na2COs loEfeO, soda,
hydrous salt and (Cu OH^COs, malachite, basic salt All carbonates
effervesce in hot acids The basic salts yield water at a high tempera-
ture only, the hydrous ones at a low temperature
The carbonates are all transparent or translucent, and all are poor
conductors of electricity, Most of them are practically nonconductors
ANHYDROUS CARBONATES
NORMAL CARBONATES
The anhydrous normal carbonates comprise the most important
carbonates that occur as minerals Most of them are included in a
single large group whose members are dimorphous, crystallizing in the
ditrigonal scalenohedral class of the hexagonal system and in the holo-
hedral division (rhombic bipyramidal class) of the orthorhombic sys-
tem. The calcium carbonate exists in three forms but only two are
known to occur as minerals
CALCITE-ARAGONITE GROUP
The relation of the dimorphs of this group to one another has been
subjected to much study, especially with reference to the two forms of
CaCQs- The orthorhombic form, aragonrie, passes into the hexagonal
form, calcite, upon heating to about 400°. At all temperatures below
970°, calcite is the stable form Moreover, while calcite crystallizes
from a dilute Solution of.CaCQa in water containing 002 at a low tem-
212
CARBONATES 213
perature, aragomte separates at a temperature approaching that of
boiling water— the more freely, the less C02 in the solution Arag-
omte crystals will also separate from a solution of calcium carbonate,
if, at the same time, it contains a gram of an orthorhombic carbonate,
or a small quantity of a soluble sulphate Some of the other carbon-
ates, for instance, strontiamte (the orthorhombic SrCCfe), pass over
into an hexagonal form like that of calcite at 700°, but again change
to the orthorhombic form upon cooling For convenience the group
is divided for discussion into the calcite division and the aragomte
division
CALCITE DIVISION
The calcite division of carbonates includes nine or more distinct
compounds and a number of well defined \aneties of these Six of the
compounds are common minerals Afl crystallize in the ditngonal
scalenohedral class of the hexagonal system and are thus isomorphous
Their most common crystals have a rhombohedral habit. The names of
the six common members with their axial ratios are:
Calcite CaCOs a c=i : 8543
Magnesite MgCOs =1 : 8095
Siderite FeCOs =i : 8191
Khodochrosite MnCOs =i • .8259
Smit\somte ZnCOs =i : 8062
There is usually also included in the group the mineral dolomite, which
is a calcium magnesium carbonate in which CaCOs and MgCOs are
present in the molecular proportions, thus MgCOs CaCOs, or
MgCa(COs)2 Its crystals are similar to those of calcite and its physical
properties are intermediate between those of calate and magnesite
Its symmetry, however, as revealed by etching is tetartohedral (rhom-
bohedral class).
The close relationship existing between the members of the group
(including dolomite) will be appreciated upon comparing the data in
the following table
Ref Indices
H
SP
Gr.
a : c
loiiAoiu
tt €
Calcite
• 3
2
73
8543
74
0
55'
I
6585
4863
Dolomite .
- 3
5-4
2
85
8322
73
o
45'
I
6817
5026
Magnesite
3-
5-45
3
04
8095
72
0
36'
I
717
515
Sidente
3
5-4
3
88
8191
73
0
o'
I
8724
6338
Rhodochrosite
3
5-45
3
55
8259
73
0
o'
I
820
5973
Srmthsonite
5
4
45
8062
72
0
20'
I
8i8±
6177
214
DESCRIPTIVE MINERALOGY
Calcite (CaCO3)
Calcite is one of the most beautifully crystallized minerals known
Its crystals are very common, and sometimes very large They are
usually colorless, though sometimes colored, and are nearly always
transparent Besides occurring in crystals the mineral is often found
massive, in granular aggregates, in stalactites, in pulverulent masses,
FIG 106
FIG 108
FEG. 107 FIG 109
FIG. 106. — Calcite Crystal with — |R, oiTa (e) and «s R, joTo (m) Nail-head Spar
FIG, 107 — Calcite Crystal with m and e Prismatic Type
FIG 108 — Calcite Ciystals with m, R», 2131 (p) and R, loli (r) Dog-tooth Spar
FIG 109 —Calcite with r, v, 4R, 4041 (M) and R8, 3251 (y)
in radial groupings, in fibrous masses and in a variety of other forms As
calate is soluble in water containing COa, it has often been found pseu-
domorphing other minerals.
Theoretically, calcite contains 56 per cent CaO and 44 per cent COg,
but practically the mineral contains also small quantities of Mg, Fe,
Mn, Zn and Pb, metals whose carbonates are isomorphous with
CaCO&
Hie forms that have been observed on calcite crystals are arranged
CARBONATES
215
in such a manner as to produce three distinct types of habit, as fol-
lows (i) the rhombohedral type, bounded by the flat rhombohedrons,
R(ioTi), — JR(oiT2) and often blunt scale-
nohedrons, like R3(2i3i) and |R2(3i45)
in which the rhombohedrons predominate
(Fig 106), (2) the pnsmatic type, with
the pnsm oo P(io7o) predominating, and
— £R(oil2) as the principal termination
(Fig 107), and (3) dog-tooth spar, contain-
ing the same scalenohedrons as on the first
type mentioned above with other steeper
ones and small steep rhombohedral planes
(Fig 108, 109, no) Nail-head spar con-
tains the flat rhombohedron — |R(oil2)
with the pnsm oo P(ioTo) (Fig 106).
Some of the crystals are very compli-
cated, belonging to no one of the distinct
types descnbed above, but forming barrel-shaped or almost round
bodies Over 300 well established forms have been identified on them.
Twins are common The principal laws are: (i) twinning plane
oP(oooi), with the vertical axis common to the twinned parts (Fig
111), (2) twinning plane — fR(oiT2), with the two vertical axes inclined
FIG no— Pnsmatic Crystals
of Calcite Terminated by
Scalenohedrons and Rhom
bohedrons from Cumber-
land, England
FIG in.
FIG 112
FIG in — Calate, R* (2131) Twinned about oP (oooi)
FIG 112 — Calcite Twin and Polysynthetic Trilling of R (ion) about — £R (0112)-
at an angle of about 52^° (Fig. 112) and (3) twinning plane R(ioTi),
with the vertical axes inclined 89° 14' (Fig. 113),
Twins of the second dass can easily be produced artificially on cleav-
age rhombs by pressing a dull knife edge on the obtuse rhombohedral
edge with sufficient force to move a portion of the mass (Fig. 114).
The change of position of a portion of the calcite does not destroy its
216
DESCRIPTIVE MINERALOGY
transparency in the least Repeated twinning of this kind is frequently
seen in marble (Fig 115), ^vhere it gives nse to parallel lamellae
The cleavage of calcite is so perfect parallel to R that crystals when
FIG 113 * FIG. 114
FIG 113 — Calcite with m, v and e, Twinned about R (loTi)
FIG 114 — Artificial Twin of Calcite, with — JR (oils) the Twinning Plane.
shattered by a hammer blow usually break into perfect little rhombo-
hedrons Its hardness is about 3 and its density 2 713 Pure calcite
is colorless and transparent, but most specimens are white or some pale
shade of red, green, gray,
blue, yellow, or even brown
or black when very impure,
and are translucent or opaque
The mineral is very strongly
doubly refracting, (see p 213)
It is a very poor conductor of
electricity.
The principal vaneties of
the mineral to which distinct
names have been given are:
Iceland spar, the trans-
parent variety used in the
manufacture of optical instru-
ments
Satin spar, a fine, fibrous
variety with a satiny luster
Limestone, granular ag-
occurnng as rock
FIG 115 —Thin Section of Marble Viewed by
Polarized Light. The dark bars are poly-
synthetic twinning lamellae Magnified 5
diameters.
masses.
Marble, a crystalline limestone, showing when broken the cleavage
faces of the individual crystals.
Ltike&apkic stone a very fine and even-grained limestone
CARBOXATES 217
Stalactites, cylinders or cones of calcite that hang from the roofs of
caves They are formed by the evaporation of dripping T\ater
Stalagmites, corresponding cones on the floors of caves beneath the
stalactites
Mexican onyx, banded crystalline calcite, often transparent.
Usually portions of stalactites
Travertine, a deposit of white or yellow porous calcite produced
in springs or rivers, often around organic material like the blades
or roots of grass.
Chalk, a fine-grained, pulverulent mass of calcite occurring in
large beds
In the closed tube calcite often decrepitates Before the blowpipe it
is infusible It colors the flame reddish yellow and after heating reacts
alkaline toward moistened litmus paper The mineral dissolves with
evolution of CO2 in cold hydrochloric acid Its dissociation tempera-
ture l is 898°, though it begins to lose C0> at a much lower temperature
The reaction with HC1, together \vith the alkalinity of the mineral
after heating, its softness and its easy cleavage, distinguish calcite from
all other minerals In massive forms it has been thought that it could
be distinguished from aragomte by heating its ponder with a httle
Co(NOs)2 solution Aragomte was thought to become violet-colored
in a few minutes while calcite remained unchanged, but recent work
proves that this test cannot be relied upon
Syntheses — Calcite crystals are obtained b\ allowing a solution
of CaCOs in dilute carbonic acid to evaporate slowly in contact with the
air at ordinary temperatures If evaporated at from 80° to 100°
ordinary temperatures, or in the presence of a httle sulphate, the ortho-
rhombic aragonite will form, Calcite is also formed by heating arag-
onite to 400-470°
Occurrence and Origin. — The mineral is widely distributed in beds,
in veins and as loose deposits on the bottoms of springs, lakes and nvers.
Its principal methods of origin are precipitation from solutions, the
weathering of calcareous minerals, and secretion by organisms.
Calcite is the most important of all pseudomorphmg agencies. It
forms pseudomorphs after many different minerals and the hard parts
of animals
Localities.— The most noted localities of .crystallized calcite are:
Andreasberg in the Harz; Freiberg, Schneeberg and other places in
Saxony; Kapnik, in Hungary, Traversella, in Piedmont, Alston Moor
1 The dissociation temperature of a carbonate is that temperature at which the
pressure of the released CO* equals one atmosphere
218 DESCRIPTIVE MINERALOGY
and Egremont, in Cumberland, Matlock, in Derbyshire, and the mines
of Cornwall, England, Guanajuato, Mexico, Lockport, N Y , Ke-
weenaw Point, Mich , the zinc regions of Illinois, Wisconsin and
Missouri, Nova Scotia, etc
Iceland spar is obtained in the Eskefjord and the Breitifjord in
Iceland Travertine is deposited from the waters of the Mammoth
Hot Springs, Yellowstone National Park It occurs also along the
River Arno, near Tivoli, Rome
Uses. — Calcite has many important uses In the form of Iceland
spar, on account of its strong double refraction, it is employed in optical
instruments for the production of polarized light Calcite rocks are
used as building and ornamental stones They are employed also as
fluxes in smelting operations, as one of the ingredients in glass-making
and in the manufacture of lime, cement, whiting, and in certain printing
operations. Limestone is also used as a fertilizer
Production — The calcite rock marketed in the United States during
1912 was valued at about $44,500,000 It was used as follows In
concrete, $5,634,000, in road and railroad making, $12,000,000, as a
flux, $10,000,000, as building and monumental stone, $12,800000,
in sugar factories, $335,000, as riprap, $1,183,000, for paving, $279,000,
and for other uses, $2,400,000 Moreover, the value of the Portland
cement manufactured during the year amounted to $67,017,000, the
quantity of lime made to $13,970,000, the value of the hydrated
lime to $1,830,000, and of sand-lime brick to $1,170,884 The quantity
of limestone required for these manufactures is not known, but it was
very great.
Magnesite (MgCO3)
Magnesite usually occurs in fine-grained white masses Crystals
are rare Pure magnesite consists of 52 4 per cent CCb and 47 6 per
cent MgO. It usually, however, contains some iron carbonate
Magnesite is completely isomorphous with calcite Its cleavage is
perfect parallel to R(ioTi). Its hardness is about 4 and the density 3 i.
The mineral is transparent or opaque. It varies in color from white
to brown, but always has a white streak Its dissociation temperature
• o
is 445 -
Magnesite behaves like calcite before the blowpipe It effervesces
in hot hydrochloric acid and readily yields the reaction for magnesia
with Co(NQs)2 It is most easily distinguished from the latter mineral
by its density, by the fact that it does not color the blowpipe flame with
the yellowish red tint of calcium and does not effervesce in cold HCL
CARBONATES 210
Synthesis — Magnesite crystals may be obtained by heating MgSO
in a solution of XajCOa at 160° in a closed tube
Occurrence and Origin — Magnesite usualh occurs in \ ems and masses
associated with serpentine and other magnesium rocks irom which it
has been formed by decomposition It is often accompanied by brucite
talc, dolomite and other magnesium compounds It has recently been
described as occurring also in a distinct bed near Mohave, CaL, inter-
stratified with cla> s and shales It is thought that in this case it ma}
have been precipitated fron* solutions of magnesium salts by Xa^COs
Localities — The mineral is found abundantly m many foreign local-
ities and at Bolton, Mass , Bare Hills, near Baltimore, Md , and in
Tulare Co., Cal , and near Texas, Penn The largest deposits are in
Greece and Hungary
Uses. — Magnesite is employed very largely in the manufacture of
magnesite bricks used for lining converters in steel works, in the lining
of kilns, etc , m the manufacture of paper from wood pulp, and in mak-
ing artificial marble, tile, etc From it are also manufactured epsom
salts, magnesia (the medicinal preparation) and other magnesium com-
pounds, and the carbon dioxide used in making soda water
Production — All of the magnesite mined in the United States comes
from California, where the yield was 10,512 tons in 1912, valued at
$105,120. Most of the magnesite used in the United States is imported
from Hungary and Greece In 1912, 14,707 tons of crude material
entered the country and 125,000 tons of the calcined product, the total
value of which ^as $1,370,000
Siderite (FeCO3)
Siderite is an important iron ore, though not as much used as formerly
It is found crystallized and massive, in botryoidal and globular forms
and m earthy masses
In composition the mineral is FeCOa, which is equivalent to 62 i
per cent FeO (48 2 per cent Fe) and 37 9 per cent COj- Manganese,
calcite and magnesium are also often present in it.
Crystals are more common than those of magnesite. They fre-
quently contain the basal plane and the steep rhombohedrons— 8R(o8Si)
and — sRfesi). R(ioli) and — |R(oiT2) are common The faces
of the rhombohedron are frequently curved. Compare (Fig 125.)
The cleavage of Siderite is like that of the other minerals of this
group. Its hardness is 3 5-4 and density 3 85. In color the mineral
is sometimes white, but more frequently it is some shade of yellow or
brown Its streak is white Most specimens are translucent.
220 DESCRIPTIVE MINERALOGY
In the closed tube siderite decrepitates, blackens and becomes mag-
netic It is only slcroly affected by cold acids but it effervesces briskly
in hot ones
Siderite is distinguished from the other carbonates by its reaction
for iron
The mineral changes on exposure into limonite and sometimes into
hematite or even into magnetite
Synthesis — Crystals of sidente may be obtained by heating a solu-
tion of FeSCU with an excess of CaCOs at 200°
Occurrence and Origin — The mineral is often found accompanying
metallic ores in veins It occurs also as nodules in certain clays and in
the coal measures. In some cases it appears to be a direct deposit from
solutions In others it is a result of metasomatism and m others is an
ordinary weathering product
Localities —The crystallized variety is found at Freiberg, in Saxony,
at Harzgerode, in the Harz, at Alston Moor, and in Cornwall, Eng-
land, and along the Alps, in Styna and Cannthia Cleavage masses
are present in the cryolite from Greenland
Workable beds of the ore are present m Columbia Co , and at Rossie,
in St. Lawrence Co , N Y , in the coal regions of Pennsylvania and
Ohio, and in clay beds along the Patapsco River, in Maryland The
massive or nodular ore from clay banks is known as ironsto? e The
impure bedded sidente interstratified with the coal shales is known
as black-band ore
Production. — Only 10,346 tons of sidente were produced in the United
States during 1912, all of it coming from the bedded deposits in Ohio
This was valued at $20,000
Rhodochrosite (MnCO3)
This mineral sometimes occurs in distinct crystals of a rose-red
color, but it is usually found in cleavable masses, in a compact form,
or as a granular aggregate Sometimes it is m incrustations It is
not of commercial importance in North America
Pure manganese carbonate containing 61 7 per cent MnO and 38 3
per cent CQs is rare The mineral is usually impure through the addi-
tion of the carbonates of iron, calcium, magnesium or zinc
The most prominent forms on crystals of rhodochrosite are R(ioYi),
— |R(oil2), ooP2(ii2o), oR(oooi) and various scalenohedrons
Its cleavage is perfect parallel to R The mineral is brittle Its
hardness is about 4 and its density about 3.55 Its luster is vitreous,
and its color red, brown, or yellowish gray. Its streak is white When
CARBONATES 221
heated it begins to lose CCb at about 320": but its dissociation temper-
ature is 632°
The mineral is infusible, but T\hen heated before the blowpipe it
decrepitates and changes color When treated in the borax bead it
gives the violet color of manganese, and \\hen fused with soda on char-
coal it yields a bluish green manganate It dissoh es in hot hydro-
chloric acid
There are but fe\v minerals resembling pure rhodochrosite m appear-
ance From all of these, except the silicate, rhodonite ip 3801, it is
distinguished by its reaction for manganese It is distinguished from
rhodonite by its hardness, its cleavage and its effervescence with acids
The impure varieties are very like some forms of siderite, from which,
of course, the manganese test will distinguish it.
Synthesis — Small rhombohedrons of rhodochrosite have been pro-
duced by heating a solution of MnSQ* with an excess of CaCCfe at 200°
in a closed tube
Occurrence and Origin — Rhodochrosite occurs in veins associated
with ores of silver, lead, copper and other manganese ores and in bedded
deposits It is the result of hydrothermal or contact metamorphism,
and of weathering of other manganese-bearing minerals
Localities. — The mineral is found at Schemmtz, in Hungary, at
Nagyag, in Transylvania, at Glendree, County Clare, Ireland, where it
forms a bed beneath a bog, at Washington, Conn , in a pulverulent
form, at Franklin, N J , at the John Reed Mine, Ahconte, Lake Co ,
and at Rico, Colo , at Butte City, Mont , at Austin, Xev., and on
Placentia Bay, Newfoundland The Colorado and Montana specimens
are well crystallized
Uses —The mineral is mined with other ores of manganese. Occa-
sionally it is employed as a gem stone.
Smithsonite fZnCO3)
Smithsomte, or "dry-bone ore," is rarely well crystallized. It
appears as druses, botryoidal and stalactitic masses, as granular aggre-
gates and as a fnable earth.
In ZnCOs there are 64 8 per cent ZnO and 35 2 per cent CCte Smith-
somte usually contains iron and manganese carbonates, often small
quantities of calcium and magnesium carbonates and sometimes traces
of cadmium A specimen from Marion, Arkansas, gave:
ZnO CdO FeO CaO CuO CCfe CdS Sift> Total
64 12 .63 .14 .38 tr. 34-68 25 06 100 26
222 DESCRIPTIVE MINERALOGY
The mineral is closely isomorphous with calcite, R(ioTi), — iR(oiT2),
4R(404i), ooR2(ii2o), oR(oooi) and R3(2i3i) being present on many
crystals The R faces are rough or curved
Its cleavage is parallel to R(ioli). Its hardness is 5 and its density
about 4 4. The luster of the mineral is vitreous, its streak is white and
its color white, gray, green or brown It is usually translucent, occa-
sionally transparent When heated to 300° for one hour it loses all of
its C02
When heated in the closed tube CC>2 is driven off, leaving ZnO as a
yellow residue while hot, changing to white on cooling The mineral
is infusible before the blowpipe If a small fragment be moistened with
cobalt nitrate solution and heated in the oxidizing flame it becomes
green on cooling When heated on charcoal a dense white vapor is
produced. This forms a yellow coating on the coal, which, when it
cools, turns white If this be moistened with cobalt nitrate and reheated
in the oxidizing flame it is colored green.
The above reactions for zinc, together with the effervescence of the
mineral in hot hydrochloric acid distinguish smithsomte from all other
compounds.
Smithsomte forms pseudomorphs after sphalerite and calcite and is
pseudomorphed by quartz, hmomte, calamine and goethite
Synthesis — Microscopic crystals of smithsomte may be produced by
precipitating a zinc sulphate solution with potassium bicarbonate and
allowing the mixture to stand for some time.
Occurrence. — Smithsomte occurs in beds and veins in limestones,
where it is associated with galena and sphalente and usually with cala-
mine (p 396) It is especially common in the upper, oxidized zone of
veins of zinc ores and as a residual deposit covering the surface of weath-
ered limestone containing zinc minerals
Localities— The mineral is found at Nerchinsk, Siberia, Bleiberg,
in Cannthia; Altenberg, Aachen, Province of Santander, Spain, at
Alston Moor and other places in England, at Donegal, in Ireland, at
Lancaster, Penn , at Dubuque, Iowa, in Lawrence and Marion Coun-
ties, Arkansas; and in the lead districts of Wisconsin and Missouri (see
galena and sphalerite).
The Wisconsin and Missouri localities are the most important ones
in North America. Here the ore occurs in botryoidal, in stalactitic
and in earthy, compact, cavernous masses of a dull yellow color incrusted
with druses of smithsonite crystals, of calamine and of other minerals,
principally of lead This is the variety known as " dry bone "
Uses — The mineral was formerly an important ore of zinc, being
CARBONATES 223
mined alone for smelting It is no\v mined only in connection with
calamine and other zinc ores, and all are worked up together. A trans-
lucent green or greenish blue variety occurring at Laurium, Greece,
and at Kelly, New Mexico, is sometimes employed for ornamental pur-
poses. About $650 worth of the material from New Mexico was utilized
as gem material in 1912
ARACOX1TE DIVISION
This division of the carbonates includes the orthorhombic (rhombic
bipyramidal) dimorphs of the members of the calcite group which,
together, form a well characterized isodimorphous group. The carbon-
ate of calcium is found well crystallized in both dmsions, but the other
carbonates are common to one only They actually occur in both divi-
sions, but they are found as .common members of one and only as
isomorphous mixtures with other more common forms in the other
Thus, barium carbonate is a common orthorhombic mineral under the
name of uithente It occurs also with CaCOs in mixed crystals under
the name bancalcite, or neotype, \*hich is hexagonal. (See also p. 212
and p 213 )
The common members of the aragonite division are:
Aragomte CaCOs Sp Gr. = 2 936 a : b : c= 6228 : i
Stronfaamte SrCOs =3 706 == 6090 : i
Witkente BaCOa =4 325 = 5949 : i
Cerussite PbCOs ac6 574 = 6102 : i 7232
Aragonite (CaCOs)
Aragomte occurs m a great variety of forms. Sometimes it is in
distinct crystals, but more frequently it is in oolitic globular and reni-
form masses, in divergent bundles of fibers or of needle-like forms, in
stalactites and in crusts.
In composition aragonite is like calcite. It often contains small
quantities of the carbonates of strontium, lead or zinc.
Crystals*are often acicular with steep domes predominating. Some
of the simplest crystals consist of oop(uo), ooP 00(010), fP 00(032),
Poo (on), 4?(44i), 9P(9Qi) and ooP2(i2o) (Fig. 116). Twinning is
common. The twinning plane is often ooP(iio). By repetition this
gives nse to pseudohexagonal forms, resembling an hexagonal prism and
the basal plane (see Figs 117 and 118), The angle no A i "10=63° 48'.
The cleavage of aragonite is distinct parallel to oo p 06 (oio) and
indistinct parallel to oo P(no). Its hardness is 3.5-4 and density about
2 93 Its luster is vitreous and its color white, often tiiigcd with gray,
7204
7266
224
DESCRIPTIVE MINERALOGY
green or some other light shade Its streak is white and the mineral is
transparent or translucent Its indices of refraction for yellow light are
a=SI j^oo, 7=1 6857 At 400° it passes over into calcite
Before the blowpipe aragomte whitens and falls to pieces Other-
wise its reactions are like those of caktte, from which it can be distin-
\
'" ui
FIG 116
FIG 117
FIG 116 — Aragomte Crystal with °o P, no (m), oo P So , oio (6) and P So , on
FIG 117 — Aragomtc Twin and Trilling Twinned about co P (no)
A
FIG 1 18— Trilling of Aragomte Twinned about <*>P (no) (A) Cross-section
(B) Resulting pseudohexagonal group, resembling an hexagonal prism and
basal plane
guished by its crystallization, its lack of rhombohedral cleavage and its
density
Synthesis —Solutions of CaCOs in dilute HaCOs form crystals of
aragomte when evaporated at a temperature of about 90° In general,
hot solutions of the carbonate deposit aragomte, while cold solutions
deposit calcite If the solution contains some sulphate or traces of
strontium or lead carbonates, mixed crystals consisting principally of
the aragomte molecule are formed at ordinary temperature,
Occurrence and Origin — Aragomte occurs in beds, usually with
gypsurn. It is also deposited from hot waters and from coid waters
CARBONATES 225
containing a sulphate (as from sea water) The pearly layer of oyster
shells and the body of the shells of some other mollusca are composed
of calcium carbonate crystallizing like aragomte Aragomte is often
changed by paramorphism into calcite, pseudomorphs of which after
the former mineral are quite common
Localities — The mineral is found at Aragon, Spain, at Bilm, in
Bohemia, in Sicily, at Alston Moor, England, and at a number of
other places in Europe It occurs in groupings of interlacing slender
columns (fios /em), m the iron mines of Styria Stalactites are abundant
at Leadhills, Lanarkshire, Scotland, and a silky fibrous variety known as
satmspar, at Dayton, England
In the United States crystallized aragomte occurs at Mine-la-Motte,
Mo , and in the lands of the Creek Nation, Oklahoma Flos fern has
been reported from the Organ Mts , New Mexico, and fibrous masses
from Hoboken, N J , Lockport, Edenville and other towns in New York
and from Warsaw, 111
Strontianite (SrCO3)
In general appearance and in its manner of occurrence strontianite
resembles aragomte Its crystals are often acicular in habit though
repeated twins are common The angle no A iTo=62° 41'
The composition of pure strontianite is SrO=7o i, C02=2g 9, but
the mineral usually contains an admixture of the barium and calcium
carbonates
Strontianite is brittle, its hardness is 3 5-4 and its density 3 7
Before the blowpipe strontianite swells and colors the flame with a
crimson tinge It dissolves in hydrochloric acid The solution im-
parts a crimson color to the blowpipe flame When treated with sul-
phuric acid it yields a precipitate of SrSO* Its refractive indices for
yellow light are a= i 5199, 7=1 668 Its dissociation temperature is
"SS°
Aragomte, witherite (BaCOs) and strontianite are so similar in ap-
pearance and in general properties that they can be distinguished from
one another best by their chemical characteristics They are all sol-
uble in hydrochloric acid and these solutions impart distinctive colors
to the blowpipe flame (see p 477)
Syntheses — Crystals of strontianite are obtained by precipitating
a hot solution of a strontium salt by ammonium carbonate, and by cool-
ing a solution of SrCOs in a molten mixture of NaCl and KC1
Occurrence, — Strontianite occurs in veins in limestone and as an
226 DESCRIPTIVE MINERALOGY
alteration product of the sulphate (celestite) where this is exposed to the
weather It is probably in all cases a deposit from water
Localities — Strontiamte is the most common of all strontian com-
pounds It frequently occurs as the filling of metallic veins It forms
finely developed crystals at the Wilhelmme Mine near Munstei, West-
phalia At Schohane, N Y , it occurs as crystals and as gianular masses
in nests in limestone It is found also at other places in New York, in
Mifflm Co , Penn , and on Mt Bannell near Austin, Texas.
Uses— Strontium compounds are little used m the arts The
hydroxide is employed to some extent m refining beet sugar and the
nitrate m the manufacture of " red fire " Othei compounds aie used
m medicine All the strontium salts used in the United States arc
imported
Witherite (BaC03)
Withente differs very little in appearance or in manner of occurrence
from aragomte Its crystals are nearly always m repeated twins that
have the habit of hexagonal pyramids (Fig.
119) The angle noAiTo«62° 46',
When pure the mineral contains 77 7 pei
cent BaO and 22 3 per cent C02
It is much heavier than the calcium car-
bonate, its density being 43 Its hardness
FIG 119— wuhcriic Twinned is 3 to 4 Its refractive mdc\ foi yellow
about COP (no), thus Im.- llght /s==I740 ils (hbboaation tenii mu-
tating Hexagonal Combina- ture Jg 0
It dissolves readily in dilute hydrochloric
acid with effervescence, and from thib solution, even when dilute, sul-
phuric acid precipitates a heavy white precipitate of BaSO-t, winch,
when heated m the blowpipe flame, imparts to it a yellowish green
color
Witherite is distinguished from the other carbonates by its crys-
tallization, and the color it imparts to the blowpipe flame.
Syntheses —Crystals are produced by precipitating a hot solution of
a barium salt with ammonium carbonate, and by cooling a molten
xnagma composed of NaCl and BaCO?
Locahfoes — Witherite is not a very common mineral in the United
States, but it occurs in large quantity associated with lead minerals in
veins at Alston Moor, in Cumberland and near Hexham, in Northum-
berland, England Some of the crystals found in these places measure
as much as six inches in length
CARBONATES
227
Its best known locality in the United States is Lexington, Kentucky,
where the mineral is associated with the sulphate, bante
Uses — It is used to some extent as a source of banum compounds
The importations of the mineral during 1912 aggregate $25,715
Cerussite (PbC03)
Cerussite generally occurs in crystals and in granular, earthy and
fibrous masses of a white coloi
The pure lead carbonate contains C02=i6 5 and PbO=835j but
the mineral usually contains in addition some ZnCOa
FIG 1 20
FIG 121
FIG 122
FIG 120 — Cerussite Crystal with cop no (w), ooPoo , 100 (0), ooPoo, oio (6),
P, in (p), oo P^, 130 (r), 2Poo, 021 (i), Pw,on (fc), JPoo, 012 (x) and
oP, ooi (c)
FIG 121 — Cerussite Tnlhng Twinned about *> P(no)
FIG 122 — Cerussite Tnllmg Twinned about «o
Its simple crystals are tabular combinations of oo P(i 10) , oo P 08 (oio)
oo Poo (100) and various brachydomes (Fig 120), and these are often
twinned in such a way as to produce six rayed stars (Fig 121), or other
symmetrical forms (Fig 122) Groups of interpenetrating crystals
are also common The angle iioAiio=620 46'.
The color of the mineral is usually white, but its surface is frequently
discolored by dark decomposition products Its luster is adamantine
or vitreous and its hardness is 3-3 5 Its density =6.5 Its refractive
indices for yellow light are a = i 8037, £ = 2 0763, 7=2 0780
The mineral is dissolved by nitric acid with effervescence and by
potassium hydroxide Before the blowpipe it decrepitates, turns yellow
and changes to lead oxide On charcoal it is reduced to a metallic
globule, and yields a white and yellow coating
228 DESCRIPTIVE MINERALOGY
Cerussite is not easily confused with other minerals It is well char-
acterized by its high specific gravity, its reaction for lead, and is dis-
tinguished from the sulphate (anglesite) by effervescence with hot acids
Syntheses —Crystals have been obtained by heating lead formate with
water in a closed tube, and by treatment of a lead salt by a solution of
ammonium carbonate at a temperature of iso°-i8o°
Occurrence and Origin — The mineral occurs at all localities at which
other lead compounds are found, since it is often produced from thes*
FIG 123 — Radiate Groups of Cerussite on Galena from Park City Distrid, Utah.
(After J M BoHlwell)
latter by the action of the atmosphere and atmospheric water It is,
therefore, usually found m the upper portions of veins
Locates —Cerussite crystals of great beauty are found m many of
the lead-producing districts of Europe and also at Phoemxville, Penn ;
near Union Bridge, m Maryland, at Austin's Mines, Wythe Co., Vir-
ginia, and occasionally in the lead mines of Wisconsin and Missouri,
In the West it occurs at Leadville, Colo , at the Flagstaff and other
mines m Utah (Fig 123), and at several different mines in Arizona.
Uses, — It is mined with other lead compounds as an ore of the metal
CARBONATES 229
Dolomite (MgCa(CO3)2)
Dolomite is apparently isomorphous with calcite but the etch
figures on rhombohedral -faces prove it to belong m the trigonal
rhombohedral class It occurs as crystals and in all the forms charac-
teristic of calcite except the fibrous
Nearly all calcite contains more or less magnesium carbonate, but
most of the mixtures are isomorphous with calcite and magnesite
When the ratio between the two carbonates reaches 5435 per cent
CaCOs 45 65 per cent MgCOs, which is equal to the ratio between
the molecular weights of the two substances, or in other words when the
two carbonates are present in the compound in the ratio of one molecule
to one molecule, the mineral is called dolomite The calculated com-
position of dolomite (MgCa(COs)2) is 30 4 per cent CaO, 217 per cent
MgO and 47 8 per cent CCte
The crystals of dolomite are usually rhombohedral combinations of
the rhombohedron R(ioli) with the scalenohedron
R3(2i3i) (Fig 124), and its tetartohedral forms,
and often the prism oop2(ii2o) and the basal
plane Its axial ratio is a:c**im 8322 Twins
are not rare, with oR(oooi) and R(ioTi) the
twinning planes The R planes are often curved,
frequently with concave surfaces (Fig 125) The
angle loli A7ioi = 730. ^ ,
rro. i i j i -j. -£ i. ni FIG 124— Dolomite
The cleavage of dolomite is perfect parallel crystal with 4R
to R The mineral is brittle Its hardness is 40^T y^ and Op'
3 5-4 and density 2 915 Its luster is vitreous or oooi (c)
pearly and its color white, red, green, gray or
brown Its streak is always white and the mineral is translucent or
transparent Its refractive indices for yellow light are w= 16817,
€= i 5026 The important varieties recognized are
Pearlspar, with curved faces having a pearly luster
Granular or saccharoidd, including many marbles and magne'San
limestones
Dolomifoc limestone, including much hydraulic limestone
Many dolomites are intermixed with the carbonates of iron, manga-
nese, cobalt or zinc and these are known as ferriferous dolomite, etc
Dolomite behaves like calcite before the blowpipe and in the closed
tube It, however, dissolves only slowly, if at all, m cold hydrochloric
acid, except when very finely powdered, though dissolving readily with
effervescence in hot acid
230 DESCRIPTIVE MINERALOGY
The reaction toward cold acid and its greater hardness easily dis-
tinguish dolomite from calcite It is distinguished from magnetite by
the flame reaction
Occurrence and Origin —Dolomite, like the calcium carbonate, occurs
crystallized m veins, and as granular masses forming gicat beds of rock
It is a precipitate from solutions and a metasomatic alteration product
of calcite
Localities — Its crystals are present at many places, among them
Bex, in Switzerland, Traversella, in Piedmont, Guanajuato, in Mexico,
Roxbury, in Vermont, Hoboken, N J., Niagara Palls, the Quarantine
FIG 125. — Group of Dolomite Crystals from Jophn, Mo Flat Rhombohedrons with
Curved Faces
Station, and Putnam, N. Y , Joplin, Mo , and Stony Pouil, N C. It
is also very widely spread as beds of dolomitic limestone
Uses — Dolomite is used for many of the purposes served by calcite,
indeed, much of the material used as marble, limestone, etc , contains a
large percentage of magnesium carbonate It is not, however, used as a
flux or m the manufacture of Portland cement, nor as a source of lime
Ankerite (Ca(Mg Fe) (003)2) is a ferruginous dolomite. It is an
isomorphous mixture of the carbonates of calcium, magnesium and iron,
in which the FeCOa replaces a part of the MgCOs in dolomite It is
usually in rhombohedral crystals, with the angle xoTi A 1101-73° 48'
Its color is white, gray or red and its streak is white Its hardness
=3 5-4, and its density = 2 98 It also occurs m coarse and fine-grained
granular masses, Ankente is infusible before the blowpipe. In the
CARBONATES 231
closed tube it darkens and when heated on charcoal it becomes mag-
netic It occurs in veins, especially those containing iron minerals
It has been found at Antwerp and other places m northern New York.
CALCIUM-BARIUM CARBONATES
Carbonates of the general composition CaBa(COs)2 occur (i) as a
series of mixed crystals isomorphous with caicite under the name hart-
calctte, (2) as a series of mixed crystals isomorphous with aragomte
known as alstomte or bromhte, and (3) a typical double salt, barytocalctte,
which is monoclmic Both alstomte and barytocaicite occur in veins
of lead ores and of bante
Barytocaicite, CaBa(COs)2 is monoclmic (prismatic class), with
a : b . c~ 7717 i 6255 and £=73° 52' It forms crystals bounded
by oo P 66 (100), ccP(no), oP(ooi), and a series of clmopyramids, of
which 2P2 (12!) and sP$ (i 5!) are common It also occurs massive Its
perfect cleavage is parallel to ooP(no) The mineral is white, gray,
greenish or yellowish Its streak is white, hardness =4 and sp gr =
3 665 It is transparent or translucent Before the blowpipe frag-
ments fuse on thin edges, and assume a pale green color, due to the
presence of a little manganese The mineral is soluble in HC1 Its
principal occurrence is Alston Moor, Cumberland, England.
BASIC CARBONATES
The basic carbonates are salts in which all or a portion of the hydro-
gen of carbonic acid is replaced by the hydroxides of metals There
are only three minerals belonging to the group that need be referred to
here Two are copper compounds One is the bright green malachite
and the other the blue azunte The composition of the former may be
CuOHv
represented by the formula ;>C03, and that of the latter by
CuOH/
CuOHv
Cu==(COs)2. Both are used to some extent as ores of the metal,
CuOH/
though their value for this purpose is not great at the present time
They may easily be distinguished from all other minerals by their
distinctive colors, by the fact that they yield water in the closed tube
and by their effervescence with acids The third mineral (hydrozincite)
is a white substance that occurs as earthy or fibrous incrustations on other
zinc compounds. Its composition corresponds to 2ZnCOs sZn(OH)2
232 DESCRIPTIVE MINERALOGY
Its hardness = 2-2 5 and its specific gravity is about 3 7 Only the two
copper compounds are described m detail
Malachite ((CuOH)2CO3)
Malachite usually occurs in fibrous, radiate, stalactitic, granular
or earthy, green masses, or as small drusy crystals covering other copper
compounds The mineral contains, when pure, 19 9 per cent CO2,
71 9 per cent CuO and 8 2 per cent KbO
Well defined crystals are usually very small monoclmic prisms (mon-
oclmic prismatic class), with an a\ial ratio 8809 • i
• 4012 and #=6i° 50' Their predominant forms
are ooPoo(ioo), ooPo>(oio), ooP(no), and
oP(ooi) Contact twins arc common, with
oo P 60(100) the twinning plane (Fig 126) The
angle no A iTo= 75° 40'
The puie mineral is bright green in color and has
a light green stieak It possesses a vitieous luster,
FIG 126 -Malachite but this becomes silky m fibrous marc* and dull
Crystal with «?, m massive specimens Crystals are translucent
no (w), ooPw, and massive pieces aic opaque. Translucent
ioo (a), and oP, pieces are pleochroic in yellowish green and dark
cot (c) Twinned green tmts Thc clcavage 1S perfcct paidud to
oP(ooi) Thc haidness of malachite is 3 5-4, and
its density about 3 9 Its refractive index, /3, for yellow light ==i 88
Malachite turns black and fuses befoic the blowpipe and tinges the
flame green With NaaCOs on charcoal it yields a copper globule. It is
difficultly soluble m pure water, but is easily dissolved m water con-
taining C02 It is soluble with effervescence in HCl and its solution
becomes deep blue on the addition of an excess of ammonia. When
heated in a closed glass tube, it gives an abundance of water. Boiled
with water it turns black and loses its COa
Malachite, on account of its characteristic color, may be easily dis-
tinguished from all other minerals but some varieties of turquoise and
a few copper compounds, such as atacamite (p 144) It may be dis-
tinguished from all of these by its effervescence with acids
Synthesis. — Malachite crystals have been obtained with the form of
natural crystals by heating a solution of copper carbonate m ammonium
carbonate
Occurrence and Origin — Malachite is a frequent decomposition
product of other copper minerals, being formed rapidly in moist places.
CARBONATES 233
It occurs abundantly in the upper oxidized portions of veins of copper
ore, where it is associated with azurite, cuprite, copper, kmomte and the
sulphides of iron and copper, often pseudomorphmg the copper minerals
The green stain noticed on exposed copper trimmings of buildings is
composed in part of this substance
Localities — The mineral occurs in all copper mines At Chessy,
France, it forms handsome pseudomorphs after cuprite In the United
States it has been found in good specimens at Cornwall, Lebanon Co ,
Penn , at Mineral Point, Wisconsin, at the Copper Queen Mine, Bisbee,
and at the Humming Bird Mine, Morenci, Arizona, and in the Tintic
district, Utah.
Uses —In addition to its use as an ore of copper the radial and mass-
ive forms of malachite are employed as ornamental stones for inside
decoration The massive forms are also sawn into slabs and polished
for use as table tops and are turned into vases, etc
Production — As malachite is mined with other copper compounds,
the quantity utilized as an ore of the metal is not known The amount
produced in the United States during 1912 for ornamental purposes was
valued at $1,085 This, however, included also a mixture of malachite
and azurite.
Azurite (Cu(CuOH)2(CO3)3)
Azurite is more often found in crystals" than is malachite. It occurs
also as veins and incrustations and in massive, radiated, and earthy
FIG 127— Azurite Crystals with oP, oot (c), -Pco, 101 (<r), ooPoo, 100 (a),
P, YII (*), oo P, no (»), -2P, 221 (A), jPa, 243 (d) and P & , on (/)
forms associated with malachite and other copper compounds. Its
most frequent associate is malachite, into which it readily alters
In composition azurite is 25 6 per cent CCh, 69 2 per cent CuO, and
5 2 per cent EfeO It changes rapidly to malachite, and sometimes is
reduced to copper
The crystals are tabular, prismatic, or wedge-shaped monochmc
forms (monochmc prismatic dass), with an axial ratio a . b : c= 8501 :
i : r 7611, and P~Bj° 36', They are usually highly modified, 58 or
234 DESCRIPTIVE MINERALOGY
more different planes having been identified on them The predominant
ones are oP(ooi), — POO(IOI), ooP(no), -2P(22i) and oopoo(ioo).
(Fig 127 ) The angle no A 1*0=80° 40'
The mineral is dark blue, vitreous, and translucent or transparent,
and is pleochroic in shades of blue It is brittle Its streak is light
blue, its hardness 3 5-4 and density 3 8 Its cleavage is distinct parallel
to Poo (on)
The blowpipe and chemical reactions for azunte are the same as
those for malachite By them the mineral is easily distinguished from
the few other blue minerals known
Synthesis — Crystals have been formed on calcile by allowing frag-
ments of this mineral to lie in a solution of CuNOj for a year or more
Occurrence — The mineral occurs in the oxidized zone of copper veins.
It is an intermediate product m the change of other coppei compounds
to malachite
Localities — Azunte occurs m beautiful crystals at Cressy, France,
near Redruth, in Cornwall, at Phoenix ville, Pcnn , at Mineral Point,
Wis , at the Copper Queen Mine, Bisbce, Aiu , at the Mammoth
Mine, Tintic district, Utah, at Hughes's Mine, California, and at many
other copper mines in this country and abroad
From Morenci, Ariz , Mr Kunz describes specimens consisting of
spherical masses composed of alternating layers of malachite and
azunte, which, when cut across, yield surfaces banded by alternations of
bright and dark blue colors
Uses — Azurite is mined with other copper minerals as an ore of cop-
per It is also used to a slight extent as an ornamental stone (see mal-
achite).
HYDROUS CARBONATES
The hydrous carbonates are salts containing water of crystalliza-
tion They are carbonates of sodium or of this metal with calcium or
magnesium Some of them occur in abundance in the waters of salt or
bitter lakes, but very few are known to occur m any large quantity in
solid form Among the commonest are:
Soda or natron Na2COa xoBfeO monochmc
Trona HNas (C0s)2 - aEfeO monoclmic
Gayliissite NagCa(C03)2 sEfeO monoclimc
Hydromagnestie Mg^OH^COaVsBfeO orthorhombic
These minerals occur either m the muds of lakes or as crusts upon the
mud or upon other minerals,
CARBONATES 235
Natron occurs only in solution and in the dry mud on the borders
of lakes
Trona, or urao, (HNa3(C03)2 2H20) is found as crystals in the
mud of Borax Lake, California, as a massive bed in Churchill Co.,
Nevada, and as thin coatings on rocks in other
places. Its crystallization is monochnic (pns- ^ c
matic class), with the axial ratio, 2 8426 : i . V 7
29494 and 18=76° 31' Its crystals are usually \ * ->
bounded by oP(ooi), ooP 66(100), -P(m) and FIG 128— Trona Ciys-
+P(Tn) (Fig 128) Fibrous and massive forms tal with oP, ooi (c),
are common The mineral has a perfect cleavage °° p * > I0° (fl) and
paraUel to oo P 60 (100) It is gray or yellowish +P' m (o)
and has a colorless streak It has a vitreous luster, a hardness of
2 5-3, and a density of 2 14 It is soluble in water and has an alkaline
taste It exhibits the usual reactions for Na and for carbonates
Gaylussite (Na2Ca(COs)2 5H20) also occurs as crystals in the
muds of certain lakes, especially Soda Lake, near Ragtown, Nevada,
and Menda Lake, Venezuela, and in clays under swamps in Railroad
Valley, in Nevada Its crystals are monochnic
(prismatic class) with a : b : c=i 4897 : i : 1 4442
and 0=78° 27' They are usually bounded by
oo P(no), P oo (on), and ^P(Ti2) (Fig 129), or by
these planes and oP(ooi) and oo P 66 (100). They
are either prismatic because of the predominance
of Pob(oii) and oP(ooi), or are octahedral m
habit because of the nearly equal development of
P ob (on) and oo P(iio). Their cleavage is perfect
FIG 1 29 -Gaylussite para]iel to ooP(no)
Crystal with oop, ^ ^^ .g ^^ ^ Uowish and trans^
no (m), Poo ,011 J
(e)and JP,Ti2 (r). lucent Its hardness is 2-3 and density 199
It is very brittle When heated m the closed
tube it decrepitates and becomes opaque It loses its water at 100°
In the flame it melts easily to a white enamel and colors the flame yellow
It is partially soluble in water, leaving a white powdery residue of CaCOs
and is entirely soluble in acids with effervescence The mineral occurs
in such large quantity in the clays underlying swamps in Railroad Valley,
Nevada, that its use has been suggested as a source of NagCOs-
CHAPTER XII
THE SULPHATES
THE sulphates are salts of sulphuric acid A large number are
known to occur in nature but many of them are dissolved in the waters
of salt lakes Of the remaining ones only a few are very common
These may be divided into an anhydrous normal group, a basic group and
a hydrated group In addition, there are several minerals that are
sulphates mixed with chlorides or carbonates
All the sulphates that are soluble in water give the test for sulphuric
acid When heated with soda on charcoal they are reduced to sulphides
The mass when placed on a silver com and moistened with a drop of
water or of hydrochloric acid partly dissolves and stains the silver dark
brown or black
The sulphates when pure are all white and transparent, and are all
nonconductors of electricity
ANHYDROUS SULPHATES
NORMAL SULPHATES
The anhydrous normal sulphates ha\c the general formula R/2S04
or R"S04 The most common ones are sulphates of the alkaline earths
and lead They belong in a single group which is orthorhombic The
few less common ones are sulphates of the alkalies or of the alkalies
and alkaline earths Only two of the latter are described*
Glauberite (Na2Ca(SO4)2)
Glaubente may be regarded as a double salt of the composition
NaaS04 CaSO/t, which requires 511 per cent Na2S04 and 48.9 per cent
CaS04 The mineral contains 22 3 per cent Na20, 20 i per cent CaO
and 57 6 per cent SOs
It nearly always occurs in monochmc crystals (prismatic class),
with an axial ratio i 2209 . i i 0270 and #=67° 49'. The most fre-
quent combination is oP(ooi), — P(ni), ooP(no), ooP 06(100),
3P3(3iT) and +P(u7), with oP(ooi) prominent (Fig 130) The
cleavage is perfect parallel to oP(ooi) The angle noAiTos=96° 58'.
236
SULPHATES
237
Glaubente is yellow, gray or brick-red m color, is transparent or
translucent and has a white streak, a vitreous luster and a conchoidal
fracture Its hardness is 2 5-3 and its specific
gravity about 28 It is brittle It is partly
soluble m water, imparting to the solution a
slight saltiness The red color of many speci-
mens is due to the presence of inclusions
Before the blowpipe the mineral decrepi-
tates, whitens and fuses easily to a white
enamel, at the same time coloring the flame FIG 130— Glaubente Crys-
yellow It is soluble m HC1 and in a large talwithoP.ooi («), <*p,
quantity of water In a small quantity of
water it is partially dissolved with loss of
transparency and the production of a deposit of
It sometimes alters to calcite
Occurrence— Glaubente is associated with rock salt and other de-
posits from bodies of salt water It is found
at Villa Rubia, m Spam, and elsewhere
in Europe, and m the Rio Verde Valley,
Arizona and at Borax Lake, California
no (m), oo P oo , 100 (a)
and — P, in (s)
FIG 131 — Thenarditc Crystal
with oo P, no (w), P, nT
(o), IPS, 106 (0 and oP,
ooi (c)
Thenardite (Na2S04) occurs as ortho-
rhombic crystals in the vicinity of salt
lakes, and m beds associated with other
lake deposits Its crystals ha\e an axial ratio 5976: i • i 2524
They are commonly prismatic but those
from California are tabular and are bounded
by ooP(uo), oP(ooi), P(iiT), £P 60(106),
and ooPw(ioo) (Fig 131) Twins are
common (Fig 132)
The mineral is colorless, white or reddish
and has a salty taste Its hardness is 2-3
and Its specific gravity 2 68 Its inter-
mediate refractive index is i 470 It is
readily soluble in water. It occurs in exten-
sive deposits in the Rio Verde Valley, Ari-
zona, and as crystals at Borax Lake, Cali-
fornia and on the shores of salt lakes in
Central Asia and South America.
FIG 132 —Thenardite
Twinned about P 06 (on)
Forms same as m Fig. 131
and oo P oo , 100 (a)
238 DESCRIPTIVE MINERALOGY
BARITE GROUP
The bante group includes the sulphates of the alkaline earths and
lead They are all light colored minerals with a nonmetallic luster
They all crystallize in the orthorhombic system (bipyramidal class),
and all have a hardness of about 4 The minerals comprising this group,
with their axial ratios, are
Anhydnte CaSO* a • b : c= 8932 ' i • i 0008
Bante BaS04 =8152 i 1 3136
Celestite SrS(>4 = 7790 i . i 2800
Angleute PbSQi = 7852 : i . i 2894
Anhydrite (CaSO4)
Calcium sulphate is dimorphous The natural compound, anhy-
drite, is orthorhombic bipyramidal In addition to this, there is another
which passes over into anhydrite when shaken for a long time with boiling
water It is produced by dehydrating gypsum at about 100° When
moistened it combines with water and passes back to gypsum It is
probably tnclmic It is unstable under the conditions prevailing at
the earth's suiface and is, therefore, not found as a mineral
Anhydrite occurs usually m fibrous, granular or massive forms, not
often in crystals When crystals occur they are commonly prismatic or
tabular m habit
In composition the mineral is 58 8 per cent SOa and 41 2 per cent
CaO
Its crystals are usually bounded by the three pinacoids oP(ooi),
oo P 60(100), oo p 06(010) and P(ni), 2P2(i2i), 3P3(i3i), POO(IOI)
and Poo (on) The prismatic types are usually elongated parallel to
the macroaxis The angle noAiTo=83° 41'
Anhydrite fuses quite easily before the blowpipe and colors the flame
reddish yellow It is very slightly soluble in water but is completely
dissolved in strong sulphuric acid It cleaves parallel to the three pm-
acoids yielding rectangular fragments. Its hardness is 3-3 5 and den-
sity about 2 93 Its luster is vitreous m massive pieces and its color
white, often with a distinct tinge of blue, gray or red. In small frag-
ments it is translucent, but in large masses it is opaque Its refractive
indices for yellow light are «= i 5693, 7=1 6130
It is distinguished from the other sulphates by its specific gravity
and the color it imparts to the blowpipe flame
SULPHATES 239
Synthesis — Its crystals have been produced by slowly evaporating a
solution of gypsum in HfoSCX
Occurrence — Anhydrite occurs as crystals implanted on the minerals
of ore veins, cis beds of granular masses associated with gypsum, and as
crystalline masses in layers associated with rock salt — the two having
been deposited by the evaporation of salt waters
Localities — The mineral is found at the salt mines of Stassfurt, in
Germany, Hail, in Tyrol, Bex, in Switzerland, in the ore veins of
Andreasberg, m Harz, Bleiberg, m Carmthia, and at many other places
m Europe At Lockport, N Y , and at Nashville, Tenn , it occurs as
crystals lining geodes m limestone, and at the mouths of the Avon and
St Croix Rivers m Nova Scotia it forms large beds associated with
gypsum
Uses — Finely granular forms of the mineral are used for ornamental
purposes, and as a medium for the use of sculptors The massive variety
is occasionally employed as a land plaster to enrich cultivated soils
Barite (BaSO4)
Bante, or heavy spar, usually occurs crystallized, though it is also
often found massive and in granular, fibrous and lamellar forms It is
a common mineral associated with sulphide ores as a gangue
The mineral is sometimes pure but it is usually intermixed with the
isomorphous calcium and strontium sulphates The pure mineral con-
tains 34 3 pei cent SOs and 65 7 per cent BaO As usually mined it
contains SiOa, CaO, MgO, AlgOa, FegOa and in some instances PbS2
(galena)
The simple crystals are usually tabular or prismatic in habit. The
tabular forms are commonly bounded by oP(ooi), ooP(no) and the
domes, P 66 (101), |P ob (102), 2P 06 (021), and P 06 (on), and sometimes
P(ni) and oo Poo (100) (Fig. 133), The prismatic forms are usually
elongated m the direction of
the a axis, and are bounded
by the same planes as the
tabular crystals (Fig 134) FlG I33 —Bante Crystals with oop, J10 (m),
Complex crystals are also iPoo, 102 (d), PoS,oii (0) and oP, ooi (c)
abundant They are often
beautifully supplied with planes, the total number known on the
species being about 100 The angle noAiio^T80 22?'
The cleavage of bante is perfect parallel to oP(ooi) and oo P(no)
It is brittle Its hardness is about 3 and its density about 4 5 The
240 DESCRIPTIVE MINERALOGY
mineral is white, often with a tinge of yellow, biown, blue, 01 red
It is transparent or opaque and its streak is white Its refi active
indices for yellow light die a= i 6369, 7= i 6491
Before the blowpipe bante decrepitates and fuses, at the same time
coloring the flame yel-
lowish green The fused
mass reacts alkaline to
lltmus paper Jt 1S m"
The mineral barite is
FIG 134 -Bante Crystals with m, d, o and c as m distinguished from the
Fig 133 Also coPoo, zoo (a), P, m 60 and ^
P2, 122 (y) l /
high specihc gravity and
the color it imparts to the blowpipe flame
Syntheses — Crystals have been made by heating precipitated barium
sulphate with dilute HC1 in a closed tube at 150°, and by cooling a fusion
of the sulphate in the chlorides of the alkalies or alkaline earths
Occurrence and Origin — Bante is a common vein-stone It con-
stitutes the gangue of many ore veins, particularly those of copper,
lead and silver. It is found also as a replacement of limestone, which,
when it weathers, leaves the barite in the form of fragments and noduleb
in a residual clay, and as a deposit in hot spnngs. In all cases it is
believed to be a deposit from solutions
Localities —Barite occurs abundantly in England, Scotland, and on
the continent of Europe Crystals are found at Cheshire, Conn ; at
DeKalb, St Lawrence Co , N Y , at the Phoenix Mine in Cxbarrus
Co,, N C , and near Fort Wallace, New Mexico Massive barite m
pieces large enough to warrant polishing is found on the bank of
Lake Ontario, at Sacketts Harbor, N Y It constitutes the filling of
veins at many different places, more particularly in the southern Appa-
lachians and m the Lake Superior region,
Preparation — Much of the mineral that enters the trade in the
United States is obtained from the deposits in residual clay The rough
material is washed, hand picked, crushed, ground and treated with
sulphuric acid. The acid dissolves most of the impurities and leaves
the powdered mineral white
Uses —The white varieties of the mineral are ground and the powder
is used in making paints The mineral is also employed in the manu-
facture of paper, oilcloth, enameled ware, and m the manufacture of
barium salts, the most important of which is the hydroxide, which is
employed m refining sugar.
SULPHATES 241
The colored massive varieties, more especially stalactitic and fibrous
forms, are sawn into slabs, polished and used as ornamental stones
Production— The quantity of bante mined in the United States
during 1912 was over 37,000 tons, valued at $153,000 The principal
producing states are Missouri, Tennessee and Virginia. The imports
in the same year were about 26,000 tons of crude material, valued at
$52,467 and 3,679 tons of manufactured material, valued at $26,848
Besides, there were imported $70,300 worth of artificial barium sul-
phate and about $280,000 worth of other barium salts, exclusive of
witherite.
Celestite (SrSO*)
Celestite occurs in tabular prismatic crystals, in fibrous and some-
times in globular masses Though usually white, it often possesses a
bluish tinge, to which it owes its name
The theoretical composition of the mineral is 43 6 per cent 80s
and 56 4 per cent SrO, but it often contains small quantities of the
isomorphous Ca and Ba compounds
Many celestite crystals are very similar in habit to those of bante.
FIG. 135 —Celestite Crystals with oo p, no (w), iPoo, 102 (<Q, J Poo, 104 (r),
oo P oo , oio (&), P oo , on (0) and oP, ooi (c)
Tabular forms are perhaps more common (Figs. 135), Occasionally,
pyramidal crystals are bounded by PiJ(i44), °oP^(ioo), Poo (on)
and oP(ooi) These often have rounded edges and curved faces and
thus come to have a lenticular shape. The angle no A iTo= 75° 50'
The cleavage of the mineral is perfect parallel to oP(ooi) and almost
perfect parallel to oo P(IIO) Its hardness is about 3 and its specific
gravity 3 95. Its luster and streak are like those of barite. Its color
is often pale blue and sometimes light red, but pure specimens are
white or colorless. Its refractive indices for yellow light are: «= i 6220,
7=1 6237
Before the blowpipe celestite reacts like barite except that it tinges
the flame crimson This crimson color may be obtained more dis-
tinctly by fusing a little powder of the mineral on charcoal in the reduc-
242 DESCRIPTIVE MINERALOGY
mg flame and dissolving the resulting mass in a small quantity of hydro-
chloric acid, then adding some alcohol and igniting the mixture
Syntheses — Crystals of celestite are produced in ways analogous
to those in which bante crystals are formed
Occurrence and Ongin —Celestite occurs in beds with rock salt and
gypsum, as at Bex, Switzerland, associated with sulphur, as at Gir-
genti, Italy, and in crystals and grams scattered through limestone,
as at Strontian Island, Lake Erie, and in Mineral Co , W Va , or
as crystals lining geodes in the same rock It is also sometimes found
as a gangue in mineral veins In some instances it was deposited by
hot waters, in others by cold waters, and in others it was concentrated
by the leaching of strontium-bearing limestones by atmospheric water
Production and Uses — Although the mineral occurs in large quan-
tity at a number of places in the United States and Canada it is not
mined A small quantity of the strontium oxide is annually imported
Strontium salts, prepared from celestite in part, aie used in the manu-
facture of fireworks and medicines and m refining sugar.
Anglesite (PbSOt)
Anglesite occurs principally as crystals associated with galena and
other ores of lead, but is found also massne, and in granular, stalactitic
and nodular forms
The theoietical composition of the mineral demands 73 6 per cent
PbO and 26 4 S03
Its orthorhombic crystals are usually prismatic or isomctnc in habit
Tabular habits are less common than in bante and celestite The
principal forms occurring are ooPcfc (100), <*>P(iio), iPoo (102), and
other macrodomes, P oo (on) and various small pyramids, with oP(ooi),
m addition, on the tabular crystals (Figs ij6, 137, 138), The angle
no A iTo=76° i6J'
The cleavage of anglesite is distinct parallel to oP(ooi) and oo P(i 10)
Its fracture is conchoidal The mineral is white, gray or colorless and
transparent, and is often tarnished with a gray coating. It has an
adamantine or residuous luster, is bnttle and has a colorless streak
Its hardness is 2 5-3 and sp gr 6 3-6 4. Impure varieties may be
tinged with yellow, green or blue shades and m some cases may be
opaque Its refractive indices for yellow light are «= i 8771, 7 « i 8937.
Before the blowpipe anglesite decrepitates It fuses m the flame of
a candle On charcoal it effervesces when heated with the reducing
flame and yields a button of metallic lead In the oxidizing flame it
SULPHATES
243
gives the lead sublimate The mineral dissolves m HN03 with dif-
ficulty
The mineral is characterized by its high specific gravity and the
FIG 136 FIG 137
FIG 136 — Ynglesilc Crystal with w P, no (m), ooPw, 100 (a), oP, ooi (c),
JP, 112 (/) and Pi, 122 (y)
FIG 137 — \nglcsitc Crystal with /;/, a and y as in Fig 136 Also oopoo,
cio (bj, P oo , on (o), P, in (s) and JP oo , 102 (d)
reaction for lead. It is distinguished from (.erussrte by the reaction for
sulphur and the lack of effervescence with HC1
Syntheses — Crystals of anglesite have been made by methods anal-
ogous to those used in the preparation of bante crystals
Occurrence — The mineral occurs as an alteration product of galena,
mainly in the upper portions of veins of
lead ores Under the influence of solu-
tions of carbonates it changes to cerus-
site
Localities —It is found in Derby-
shire and Cumberland, in England,
near Siegen, in Prussia, m Australia and
in the Sierra Mojada, m Mexico In the
United States crystals occur at Phoenix-
ville, Penn , in the lead districts of the Mississippi Valley, and at
various points in the Rocky Mountains
Use*. — It is mined with other lead compounds as an ore of this metal
BASIC SULPHATES
Although several basic sulphates are known as minerals, only two
are of importance One, brochantite, is a copper compound found, with
other copper minerals, in the oxidized portions of ore veins, and the
other, alumte, is a double salt of aluminium and potassium. This min-
FIG 138 —Anglesite Crystal with
m, y, c and d as in Figs 136 and
137 Also iP 63 , 104 (Q and P?,
144 (x)
244 DESCRIPTIVE MINERALOGY
eral is one of a series of compounds forming an isomorphous group, with
the general formula (R'"(OH)2)6R'2(S04)4 or (R'''(OH)2)oR''(SOi)i,
in which R'"=A1 or Fe, R'2=K2, Na2 or H2 and R"=Pb
Alumte ((A1(OH)2)6K2(S04)4)
Alunite, or aiumstone, is a comparatively rare mineral, but, because
of its possible utilization as a source of potash, it is of considerable in-
terest It has long been used abroad as a source of potash alum
The mineral, when pure, contains 38 6 per cent 863, 37 o per cent
Al20s, ii 4 per cent K20 and 13 o per cent EkO, which corresponds to
the formula given above, or if written in the form of a double salt
3(A1(OH)2)2S04 K2S04 The chemical composition of a crystalline
specimen from Marysville, Utah, is as follows
S03 Al20j Fe203 P20f, K20 Na20 H20+ H20- Si02 Total
38 34 37 18 tr 58 xo 46 33 12 90 09 22 too 10
Alunite occurs in hexagonal crystals (ditrigonal scalenohedral class),
with an axial ratio of i i 252 The natural crystals are nearly always
simple rhombohedrons, R(ioTi), or R modified by other rhombohedrons
and the basal plane Because the angle between the rhombohcdral
faces is about 90° (90° 50') , the habit of the crystals is cubical The
mineral also occurs massive, with fibrous, granular or porcelain-like
structure
Alunite is white, pink, gray or red, and has a white streak It is
transparent or translucent and has a vitreous or nearly pearly luster.
Its cleavage is distinct parallel to oP(oooi), and it has an uneven, con-
choidal or earthy fracture Its hardness ib 3 5-4 and its density =
26-275. Its indices of refraction for yellow light are: €sasiS92,
<o=i 572
Before the blowpipe the mineral decrepitates, but is infusible In
the closed tube it yields water and at a high temperature sulphurous and
sulphuric oxides Heated on charcoal with Co(NOs)2 it gives the blue
color characteristic of Al20a It also gives the sulphur reaction It is
insoluble in water but is soluble in H2S04 When ignited it gives off
all its water and three-quarters of its S04, the other quarter remaining
in &2S04 When the igmted residue is treated with water, the potas-
sium sulphate dissolves and insoluble Al20s is left. It is upon this
latter reaction that the economic utilization of the mineral depends,
The mineral is characterized by its color and hardness together
with the reactions for AljHgO and sulphuric acid
SULPHATES 245
Synthesis — Crystals have been made by heating an excess of alu-
minium sulphate with alum and water at 230°
Occurrence anl Ongm— The mineral occurs m seams or veins in
acid lavas It is thought to have been formed in some instances by
the action of sulphurous vapors upon the rock forming the vein walls,
in other instances by direct precipitation from ascending magmatic
waters, and in others by the action of descending BfeSC^
Localities — The principal known occurrences of alumte are at
Tolfa, Italy, at Bulla Delah, New South Wales, on Milo, Grecian
Archipelago, and at Mt Dore, France
In the United States it is found with quartz and kaolin in the
Rosita Hills, and the Rico Mts,, Colo , in the ore veins at Silverton
and Cripple Creek, Colo , as a soft white kaolin-like material in the
ore veins at Goldfield, Nev , as a crystalline constituent in the rocks
at Goldfield, Nev , and Tres Cerntos, Cal , and in the form of a great
vein of comparatively pure material at Marysville, Utah
Uses — In Australia alumte is calcined and then heated with dilute
sulphuric acid. The mixture is then allowed to settle and the clear
solution is drawn off and cooled Alum crystallizes The mother liquor
which contains aluminium sulphate, after further treatment with the
calcined mineral, is evaporated and the aluminium salt separated by
crystallization In the United States it is now (1916) being utilized
as a source of potash and aluminium
Brochantite ((CuOH)2S04 2Cu(OH)2) occurs in groups of small
prismatic crystals, in fibrous masses and in drusy crusts Its crystal-
lization is orthorhombic with a b • £-.7739 • i ; 4871 and the angle
1 10 A no =75° 28' Cleavage is perfect parallel to oopas (oio). The
mineral is emerald-green to blackish green and its streak is light
green. It is transparent or translucent, and its luster is vitreous,
except on cleavage planes where it is slightly pearly Its hardness is
3 5-4 and density 3 85 In the closed tube it decomposes, yielding
water and, at a high temperature, sulphuric acid. It gives the usual
reactions for copper and sulphuric acid Brochantite occurs in the
upper portions of copper veins at many places, in some of which it was
formed by the interaction between silicates and solutions of copper
salts. In the United States it has been foi}nd at the Monarch Mine,
Chaffee Co , Colorado, at the Mammoth Mine, Tmtic District, Utah,
and in the Clifton-Morenci Mines, Arizona,
246 DESCRIPTIVE MINERALOGY
HYDROUS SULPHATES
The hydrous sulphates comprise a numbei of sulphates combined
with water Among them are the normal salts miralnhte or glauber
salt (Na2S04 loEfeO), gypsum (CaSQi 2H/)), the epwmilc and inclan-
tertte groups (R//S04 7H20), chakanttnte (CuS04 sEbO), «md the
alum group (R'A1(S04)2 i2H20), kiesente (MgSOi H2O), polyhalite
(K2MgCa2(S(X)4 H20), and a number of basic compounds Several
of them are of considerable economic importance, They are separated
into a normal group and a basic group,
HYDRATED NORMAL SULPHATES
The hydrated normal sulphates occur in crystals, and most of them
are found also in beds mterstratified with other compounds that arc
known to have been precipitated by the evaporation of sea water or the
water of salt and bitter lakes All are soluble in water
Mirabdite, or glauber salt, (Na2SOt loHaO) is a white, trans-
parent to opaque substance occurring m monoclmic crystals or as
efflorescent crusts Its hardness is i 5-2 and specific gravity i 48 It
is soluble in water and has a cooling taste When exposed to the air it
loses water and crumbles to a powder Mirabihte occurs at the hot
springs at Karlsbad, Bohemia and is obtained from the water of many
of the bitter lakes m California and Nevada Its crystals are deposited
from a pure solution of Na2S04 If the solution contains NaCl, how-
ever, thenardite (Na2S04) deposits
Kieserite (MgS(>4 H20) occurs commonly m granular to compact,
massive beds mterstratified with halite and other soluble salts at Stass-
furt, Germany, and at other places where ocean water has been evap-
orated. It is believed to have resulted from the partial desiccation of
epsomite (MgS04 ?H20), though it may be deposited from a solution
of MgSO* m the presence of MgCfe. Kiesente is white, gray, or yellow-
ish, and is transparent or translucent It forms sharp bipyraimdal
monoclmic crystals Its hardness is 3 and its density 2 57* In the
presence of water it passes over into epsomite and dissolves, yielding a
solution with a bitter taste. Large quantities are utilized in the fer-
tilizer industry
When exposed to the air it becomes covered with aa opaque crust*
SULPHATES
247
Gypsum (CaSO4 2H20)
Gypsum is the most important of all the hydrous sulphates It
occurs in massive beds a'vociated with limestone, m crystals, in finely
granular aggregates and in fibrous masses, under a great variety of
conditions
Theoretically, it consists of 46 6 per cent 80s, 32 5 per cent CaO and
20 9 per cent EfeO, but usually it contains also notable quantities of other
components, especially Fe203, AbOa and 8162 Clay is a common im-
purity in the massive varieties
The analyses of two commercial gypsums follow
CaSCXt H20 Si02 A1203 CaC03 MgC03 Total
78 40 19 96 35 12 56 57 99 96
78 51 20 96 05 08 ii 99 71
Dillon, Kans
Alabaster, Mich
The crystals are monoclmic (prismatic class), with a : b • ^=.6895 :
i • 4132 and j8=8i° 02' They are usually developed with a tabular
habit due to the predominance of oo P OD (oio) The prism oo P(iio),
FIG 139 FIG 140
FIG 139 — Gypsum Crystals with wP, no («), ooPoo, oio (ft), — P, in (/) and
FIG 140 — Gypsum Twinned about oo P 55 (100) Swallow-tail Twin Form mt
I and b as in Fig 139
and pyramid +P(ixI) are also nearly always present (Fig 139). Often
the +P faces are curved, producing a lens-shaped body Twinning is
very common, giving rise to two types of twinned crystals In the most
common of these oo P 56 (100) is the twinning plane and the resulting
twin has the form of Fig 140 In the second type -P 66 (101) is the
twinning plane (Fig. 141) Forms of this type are frequently bounded
by +P(iiT), -P(iii), |P oo (103), and °OP65 (100) When the side
248
DESCRIPTIVE MINERALOGY
faces are curved the well known arrowhead twins result (Fig 141)
The angle noAiTo=68° 30'
The mineral possesses a good cleavage parallel to oo P $> (oio)
yielding thin inelastic fohae, another parallel to +P(Tn) and a less
perfect one parallel to oo P 66 (100)
It is white, colorless and transpar-
ent when pure, gray, icd, yellow,
blue or black when impure Its
hardness is i 5-2 and sp. gr =2 32
The luster of crystals is pearly on
oo P ob (oio) and on other surfaces
vitreous Massive varieties are often
dull The refractive indices for yel-
low light are, a= 1.5205, 0= 1.5226,
FIG 141— Gypsum Twinned about ^*~J S29
-P«5(ioi) Forms <*>POO, 100 In the closed tube the mineral
(a), -P, in (/), P, nl («) and gives off watei and falls into a white
J P 55 , Io3 (e) Arrow head Twm powder (see p 238) It colors the
flame yellowish red and yields the sul-
phur test on a silver coin. It is soluble m about 450 pts of water and
is readily soluble in HC1 When heated to between 222° F and 400° F
it loses water and disintegrates into powder, which, when ground,
becomes " plaster of Pans " This, when moistened with water, again
combines with it and forms gypsum The crystallization of the mass
into an aggregate of interlocking crystals constitutes the " set."
Gypsum is distinguished from other easily cleavable, colorless min-
erals by its softness and the reactions for S and EfeO.
The varieties of gypsum generally recognued are.
Syenite, the transparent crystallized variety,
Safanspar, a finely fibrous variety,
Alabaster, a fine-grained granular variety, and
Rock-gypsum, a massive, structureless, often impure and colored
variety.
Gypsiie is gypsum mixed with earth
Syntheses — Crystals of gypsum separate from aqueous solutions of
CaSO* at ordinary temperatures, and also from solutions saturated
with Nad and MgCk Some of these are twinned.
Occurrence and Origin — Gypsum forms immense beds interstrati-
fied with limestone, clay and salt deposits where it has been precipitated
by the evaporation of salt lakes Its crystals occur around volcanic
vents, where they are produced by the action of sulphuric acid on cal-
SULPHATES 249
careous rocks. They are also found isolated in clay and sand, and in
limestone, wherever this rock has been acted upon by the sulphuric acid
resulting from the weathering of pynte Gypsum also occurs in veins
and is found in New Mexico in the form of hills of wind-blown sand
Localities — Crystals are found m the salt beds at Bex, Switzerland,
in the sulphur mines at Girgenti, Sicily, and at Montmar-tre, France
In the United States they occur at Lockport, N Y , in Trumbull Co ,
Ohio, and in Wayne Co , Utah, in limestone, and on the St Mary's
River, Maryland, in clay
Extensive beds occur in Iowa, Michigan, New York, Virginia, Ten-
nessee, Oklahoma and smaller deposits in many other states, and wind-
blown sands in Otero Co , New Mexico
Uses — Crude gypsum is used in the manufacture of plaster, as a
retarder in Portland cement, and as a fertilizer under the name of land
plaster The calcined mineral is used as plaster of Pans and in the
manufacture of various wall finishing plasters, and certain kinds of
cements Small quantities are used in glass factories, and as a white-
wash, a deodorizer, to weight phosphatic fertilizer, as an adulterant in
candy and other foods, and as a medium for sculpture
Production — The quantity of gypsum mined in the United States
during 1912 aggregated 2,500,757 tons, valued at $6,563,908 in the form
in which it was sold Of this amount, 441,600 tons of crude material,
valued at $623,500 were sold ground, and 1,731,674 tons, valued at $5,-
940,409, were calcined The output of New York was valued at $1,241,-
500, that of Iowa at $845,600 and of Ohio at $812,400
After the United States the next largest producer is France with a
product in 1910 of 1,760,900 tons, valued at $2,942,600 and Canada with
525,246 tons, valued at $934,446
EPSOMITE AND VITRIOL GROUPS
These groups comprise minerals with the general formula RSO-i 7HkO,
in which R=Mg, Zn, Fe, Ni, Co, Mn and Cu Isomorphous mix-
tures indicate that the compounds are diomorphous, and that the
group is, therefore, an isodimorphous group. The group is separable
into two divisions, of which one, the epsomite group, crystallizes in the
bisphenoidal class of the orthorhombic system with axial ratios approx-
imating i : i ' ,565 The other division, the vUriol9 or mdanterite,
group crystallizes in the prismatic class of the monochmc system with
axial ratios approximating 1 18 ' i ' i 53 and ft approximating 75°
Only the magnesium compound among the pure salts is known to crys-
tallize in both systems. Crystals separated from a saturated solution
250 DESCRIPTIVE MINERALOGY
are orthorhombic, while those separated from a supersaturated solution
are monoclimc Other salts occur in isomorphous mixtures in both
systems All members of the group are soluble in water and all occur as
secondary products formed by decomposition of other minerals.
Epsomite (MgSO4 7H20)
Epsomite, or Epsom salt, usually occurs in botryoidai masses and
fibrous crusts coating various rocks over which dilute magnesium sul-
phate solutions trickle, and mingled with earth
in the soils of caves The solutions result from
tke act10n upon magnesian rocks of sulphuric
c,cid derived from oxidumg sulphides Crys-
tals are rare
The composition corresponding to MgSOr
yHkO demands 32,5 SOa, 163 MgO and 51 2
H20
The mineral forms white or colorless bi-
Ho 142-EpsomitcCrys- sphenoidalj orthorhombic crystals, with an
tal with OQ P 1 10 (m) , , . -,,
p axial ratio a b ' c= 9901 i S7°9 Their
and -r, in (s) habit is tetragonal The angle no A 1^0=89°
26' The commonest forms occurring on syn-
P P
thetic crystals are combinations of ooP(iio), and -T(III) or -~J(ni)
2 2
(Fig 142) Natural crystals contain, m addition oo P 56 (oio) and
POO(IOI)
The luster of epsomite is vitreous, its hardness 2 0-2 5 and specific
gravity 170 Its refractive indices for yellow light are a —143 25,
0=i 4554 and 7= i 4°°8
The mineral is soluble m water, yielding a solution with a bitter taste
With a solution of barium chloride it yields a white precipitate of BaSOt
Epsomite is distinguished from other colorless, soluble minerals by
its taste and the reactions for S and Mg
Synthesis —Crystals are produced by evaporation of solutions of
MgSO* containing certain other salts From those containing borax,
crystals of the type indicated above are separated The production ot
right or left crystals may be provoked by inoculation of the solution with
a particle of a crystal of the desired type
Locakties — Epsomite occurs m mineral waters, as, for instance, at
Seidlitz, Bohemia, on the walls of mines and caves, among the deposits
of bitter lakes, and as crystals m the soil covering the 'floors of caves
SULPHATES 251
Melantente, 01 copperas (FeSO4 7H20), is usually m fibrous,
stalactitic or pulverulent masses associated with pynte or other sul-
phides containing iron, from which it was produced by weathering
processes It is commonly some shade of green Its streak is colorless
Its crystals, which are monochmc (prismatic class), are rare The
mineral has a hardness of 2 and a density of i 9 It is soluble in water,
forming a solution which has a sweetish astringent taste.
ALUM GROUP
The alum group includes a large number of isomorphous compounds
with the general formula R'A1(S04)2 laHsO The group crystallizes
in the isometric system (dyakisdodecahedral class), but all of its mem-
bers are so readily soluble m water that they are rarely found in nature
The commonest alums are kalmite (KA1 (864)2 I2H20) and soda alum
(NaAl(S04)2
DOUBLE SULPHATES WITH CARBONATES OR CHLORIDES
A number of compounds of sulphates with chlorides and carbonates
are known, but of these only one is of any great economic importance
Two others afford interesting crystals The commercial compound is
kaimte, which is a hydrated combination of MgS04 and KC1, with
the formula M&S04 KC1 3H20 The other two best known members
of the group are leadhillile (PbSO4 Pb(PbOH)2(COs)2 and hanksite
(2Na2C03 QNa2S04 KCI)
Kainite (MgSO4 KCI 3H20)
Kaimte is found only in beds associated with halite and other deposits
from saline waters It is rarely crystallized Crystals are monoclmic
(prismatic class), with a b c=i 2186 : i . 5863 and £=85° 6'. They
possess a pyramidal habit with oP(ooi) and dbP(ni)(iiT) predom-
inating
The mineral usually forms granular masses which are white, yellow,
gray or red It is transparent, has a hardness of 2 and sp gr 2.13,
and is easily soluble in water Its refractive indices for sodium light are-
01=14948 and 7*1.5203
When heated in a glass tube it yields water and HC1 It is distin-
guished from other soluble minerals by this reaction, and by the fact
that it yields the test for sulphur, and colors the flame blue when its
powder is mixed with CuO and heated before the blowpipe
252 DESCRIPTIVE MINERALOGY
Synthesis — Crystals have been produced by evaporating a solution
of K2S04 and MgSOi containing a great excess of MgCb
Occurrence — Kaimte occurs in the salt beds of Stassfurt, Germany,
and of Kalusz in Gahcia, and in the deposits of salt lakes and lagoons
It also occurs as crusts on some of the lavas of Vesuvius
Uses.— The mineral is utilized as a source of potassium m the manu-
facture of potassium salts and fertilizers Large quantities are imported
annually into the United States In 1912 the imports aggregated
485,132 tons, valued at $2,399,761
Hanksite (2Na2CO3 pNa2SOi KC1) occurs almost exclusively in
. hexagonal prisms that are prismatic or tabular,
or in double pyramids suggesting quartz crys-
tals Their axial ratio is i . i 006 The com-
monest crystals are bounded by oP(oooi),
FIG 143— Hanksite Crys- ooP(ioTo), P(ioTi) (Fig. 143) and 2P(202i),
tal with OOP, joio (w), or |p(4o4s) Their cleavage is imperfect
P, ion (0) and oP, oooi p^M ^ op(oool) Thc mmeml fe whjte Qr
yellow Its hardness -2 and its specific
gravity =256 It is soluble m water. Its refractive indices are
w=i 4807 and €=i 4614 It occurs at Borax Lake and Death Valley,
California, in the deposits of salt lakes
LeadhUlite (PbSO4 Pb(PbOH)2(CO,<02) occurs principally as
crystals m the oxidized zones of lead and silver veins The crys-
tals are monoclmic (prismatic class), and have an hexagonal habit.
Their axial ratio is i 7515 11:2 2261. j9=89°32'. The principal
forms observed on them are oP(ooi), oo'P(no), ooP<w (too), P(m)
and £P6o (102) In the most common twins ooP(no) is the twin-
ning plane The mineral is white or yellow, green or gray, and it is
transparent or translucent Its streak is colorless It is sectile, has a
hardness of 2 5 and a specific gravity of 6.35 Before the blowpipe it
mtumesces, turns yellow, and fuses easily (i 5) Upon cooling it again
becomes white It effervesces m HNOs and leaves a white precipitate
of PbS04 It reacts for sulphur and water It is found at Leadhills,
Scotland, and Mattock, England, associated with other ores of lead;
at a lead mine near Iglesias, Sardinia, and at several silver-lead mines
in Arizona.
CHAPTER XIII
THE CHROMATES, TUNGSTATES AND MOLYBDATES
THE CHROMATES
The only chromate of importance, among minerals, is the lead salt of
normal chromic acid, HkCrO* There are several other chromates
known, but they are basic salts and are rare All are lead compounds
The normal salt, PbCrO*, is known as crocoite Chromic acid is un-
known, as it spontaneously breaks down into CrOa and water when set
free from its salts Its best known compound is potassium chromate,
Crocoite (PbCr04)
Crocoite is well characterized by its hyacinth-red color It is a lead
chromate with PbO=68 9 per cent and 003=31 i per cent.
Its crystallization is monoclmic
(prismatic class) with a . b : c
= 9603 : i . 9159 and 0=77° 33'-
Its crystals, which are usually im-
planted on the walls of cracks in
rocks, are prismatic or columnar
parallel to ooP(no) Their pre-
dominant forms are ooP(no),
— P(iu), and various domes (Fig
144). Their* cleavage is distinct
parallel to ooP(uo) The angle
1 10 A no=860 19' The mineral
also occurs in granular masses
Crocoite is bright hyacinth-red,
and is translucent Its streak is
orange-yellow The mineral is sec-
tile Its fracture is conchoidal, its
hardness 2.5-3 and density about 6
is about 2 42,
In the closed tube it decrepitates, and blackens, but it reassumes its
red color when heated On charcoal it deflagrates and fuses easily,
253
FIG 144 —Crocoite Crystals with «>P,
no (m), cop}, 120 (/), -P, in 0),
3Po5, 301 (*), PS5, Tor (£), oP,
001 (C), P«>,OII (*), 2? CO, 021 (?)
and iPSb,oi2 (w)
Its intermediate refractive index
254 DESCRIPTIVE MINERALOGY
yielding metallic lead and a lead coating With minocosmic salt it
gives the green bead of chromium
The mineral is easily lecogmzed by its color and the test for chro-
mium
Synthesis — Crystals, like those of crocoite, have been obtained by
heating on the water bath a solution of lead nitrate in nitric acid and
adding a dilute solution of potassium bichromate
Occurrence — Crocoite occurs under conditions which suggest that it
is a product of pneumatolysis
Locahhes — It is found in the Urals, at Rezbanya and Moldawa, m
Hungary, m Tasmania, and m the Vulture Mining district, Mancopa
Co , Arizona,
THE TUNGSTATES AND MOLYBDATES
The tungstates are salts of tungstic acid, EfoWC^ They are the
principal sources of the metal tungsten which is beginning to have im-
portant uses The molybdates are salts of molybdic acid, liaMoOt
The two most prominent tungstates arc ideditc, CaWQi, and wolf-
ramite (Fe Mn)W04, and the most prominent molybdate is wulfenite,
PbMoO*
All tungsten compounds give a blue bead with salt of phosphorus in
the reducing flame When fused with NagCOa, dissolved in water
and hydrochlonc acid, and treated with metallic zinc (see pp 482, and
492 for details of test), they also yield a blue solution which rapidly
changes to brown
The molybdates give with the salt of phosphorus bead in the oxidis-
ing flc,me a yellow-green color while hot, changing to colorless when cold.
In the reducing flame the color is clear green.
SCHEELITE GROUP
The scheelite group comprises a series of tungstates and molybdates
of Ca, Cu and Pb The minerals arc tetragonal and hcmihcdral and
are all well crystallized The more important members of the group
are scheehte and wulfemte CuprotungMe is a copper tungstate (CuW04)
and stolzite a lead tungstate
Scheelite
The formula of scheelite demands 80 6 per cent WO.?, and 194 per
cent CaO, but the mineral usually contains a little molybdenum in
place of some of the tungsten It nearly always contains also a little Fe.
CHROMATES, TUNGSTATES AND MOLYBDATES 255
Scheehte crystallizes in the tetragonal bipyraimdal class Its crys-
tals are usually pyramidal, though often tabular m habit Their axial
ratio is i : i 5268 On the pyramidal types the predominant planes
are pyramids of the first, second (Fig 145), and third orders and on the
tabular types, in addition, the basal plane One of the most familiar
combinations is P(m),P co (101), y (313) and | ^lj(i3i) (Fig 145),
Other forms frequently found on its crystals are |P oo (102) and £P °°
(105) The angle no A In = 79° SSi' Twinning is common, both
contact and penetration twins having oo p oo (100) as the twinning
plane The mineral aJbO occurs m remform and granular masses
Scheehte is white, yellow, brown, greenish or reddish, with a white
FIG 145 FIG 146
FIG 145 — SdiceliLc CryoUl with P, in \pjt P oo , 101 (e) and oP, ooi (c),
FIG 146 — Scheehte Crybtal with 1> and e as in Fig 145 Also I ~ I , 313 (h) and
streak and vitreous luster It has a distinct cleavage parallel to P(ooi),
and an uneven fracture It is brittle, has a hardness of 4 3-5 and a
density of about 6, and is transparent or translucent It is soluble in
HC1 and HNOs with the production of a yellow powder, tungsten tri-
oxide, which is soluble m ammonia Its refractive indices are €= i 9345,
w= i 9185 for red light
Before the blowpipe the mineral fuses to a semitransparent
glass With borax it forms a transparent glass which becomes opaque
on cooling With salt of phosphorus it yields the characteristic beads
for tungsten, but specimens containing iron must be heated with tin on
charcoal before the blue color can be developed
Scheehte is distinguished from limestone, which its massive forms
closely resemble, by its higher specific gravity and the absence of effer-
256 DESCRIPTIVE MINERALOGY
vescence with HC1 From quartz it is distinguished by its softness and
from bante by greater hardness and higher specific gravity
Syntheses —Crystals of scheehte have been made by adding a solu-
tion of sodium tungstate to a hot acid solution of CaCk, and by fusing
the two compounds They have also been produced by fusing wolfram-
ite with CaCl2
Occurrence and Origin — Scheehte is found m gold-quartz veins
and in veins cutting acid igneous rocks, where it is associated with
cassiterite, topaz, fluorite, molybdenite, wolframite and many other
metallic compounds, and as a contact metamorphic product in altered
limestone intruded by granite It is probably m all cases a deposit
from hot solutions
Localities — It occurs at Zinnwald, Bohemia, Altenbeig, Saxony,
Carrock Fells, Cumberland, England, Pitkaranta, Finland, in New
Zealand, and in the United States at Monroe and Trumbull, Conn , in
the Atoha District, Kern Co , California, the Mammoth Mining Dis-
trict, Nevada, in Lake County, Colorado, near Gage, New Mexico,
where it occurs with pynte and galena in a vein cutting limestone,
and in the placer gravels at Nome, Alaska
Uses of Tungsten —Tungsten is used puncipally m the manufacture
of tool steel, electric furnaces and targets for Ronlgen rays It is
employed also as filaments m electric-light bulbs, in the manufacture
of sodium tungstate which is used for fireproofing cloth, as a mordant
in dyeing, and for a number of other minor purposes
Production — Scheehte has been mined in small quantity m Idaho,
Alaska, California, Nevada, Arizona, and New Mexico, Us a source of
tungsten, but most of this element has heretofore been produced from
other compounds, mainly wolframite In 1913 a few hundred tons of
scheehte concentrates were produced m the Atoha district, California,
and the Old Hat district, near Tucson, Ariz. At present (rgi6) it is
being produced in large quantity near Bishop, Inyo Co., Cal.
Stolzite (PbWO4) is completely isomorphous with wulfenite. Its
crystals, which are pyramidal or short columnar, arc mainly combina-
tions of °oP(no), P(in), 2P(22i) and oP(ooi) Their axial ratio is
i . i 5606
The mineral is gray, brown, green or red. It is translucent and
has a white streak Its hardness is 2 75-3 and its sp. gr 7.87-8.23.
Its refractive indices for yellow light #re- w =2 2685, € = 2 182
Before the blowpipe it decrepitates and melts to a lustrous crystal-
line globule. The bead with microcosmic salt in the reducing flame
CHROMATES, TUNGSTATES AND MOLYBDATES 257
is blue when cold, in the oxidizing flame it is colorless The mineral
is decomposed by HNOs leaving a yellow residue ol WOs Crystals
have been made by fusing sodium tungstate and lead chloride
Its principal localities are the tm-bearing veins at Zmnwald, Bo-
hemia, the copper veins in Coquimbo, Chile, and Southampton, Mass ,
where it is associated with other lead compounds
Wulfenite (PbMoO4)
Wulfemte is the only molybdate of importance that occurs as a
mineral Its formula demands 39 3 MoOs and 60 7 PbO Calcium
sometimes replaces a part of the Pb and tungsten a part of the Mo.
Wulfemte is hemihedral and hemimorphic (tetragonal pyramidal
class) Its crystals are more frequently tabular than those of scheelite,
and they are usually very thin
The mineral, however, occurs also m pyramidal and prismatic crys-
tals which, in some cases, exhibit distinct hemunorphism Their axial
Fro 147 FIG 148
FIG 147 — Wulfemte Crystal with °o P <*> , 100 (a) and ^P °o , i o 12 (0)
FIG 148 — Wulfenite Crystal with oP, ooi (c), JPoo, 102 («), P°°, 101 (e),
P, in (M) and JP, 113 (s)
ratio is a ' c=i . i 5777 The most common forms found on its crys-
r oo pal
tals are oP(ooi), P(ni), —j1 (320), fP(ii3) and POO(IOI) (Fig
147 and 148). The angle in /\1n = So° 22'.
The cleavage, parallel to P, is very smooth, and the fracture is con-
choidal The mineral is brittle Its hardness is about 3 and specific
gravity about 6 8 Its luster is resinous or adamantine, and its color
orange-yellow, olive-green, gray, brown, bright red or colorless Its
streak is white and it is transparent For red light, o>= 2 402, e= 2 304
Before the blowpipe wulfenite decrepitates and fuses readily With
salt of phosphorus it gives the molybdenum beads With soda on
charcoal it yields a lead globule. When the powdered mineral is evap-
orated with HC1 molybdic oxide is formed On moistening this with
water and adding metallic zinc an intense blue color is produced.
Wulfenite is distinguished from tanadmtte (p 271), by crystalliza-
tion, by the test for chlorine (vanadimte) and the test for tungsten.
258 DESCRIPTIVE MINERALOGY
Synthesis — Wulf emte crystals have been produced by melting
together sodium molybdate and lead chloride
Occurrence and Localities — The mineral occurs in the oxidized zone
of veins of lead ores at some of the principal lead occurrences in Europe,
and in the United States near Phoenixville, Pennsylvania, in the Organ
Mountains, New Mexico, at the mines in Yuma County, Arizona, at
the Mammoth Mine, m Pmai County in the same State, and at many
other of the lead mines m the Rocky Mountain states
Uses — Wulfenite is an important source of molybdenum, but,
because of the few uses to which this metal is put, the amount of wulfen-
ite mined annually is very small
WOLFRAMITE GROUP
Wolframite ((Fe MnJWO*)
Wolframite is the name given the isomorphous mixtme of the man-
ganese and iron tungstates that occur neaily puu* in some vanctics
of the mineials hubnente and fcrbente
The mixture of the uon and manganese molecules is more common
than either alone, consequcntl} wolframite is the commonest member of
the group. The properties of all three mmcials, ho\ve\cr, arc so nearly
alike that they must be distinguished by chemical analysis
The name wolframite is usually applied to mixtures of the tungstates
in which the proportion of Fe to Mn \uries between 4 : i and 2 • 3, or
between g 5 per cent and 189 per cent of FeO and 14 pci cent and
4 7 per cent of Mn02.
It has recently been suggested that the name ferbente be limited
to mixtures containing not more than 20 per cent of the hubnente mole-
cule and the name hubnerite to those containing not more than 20 per
cent of the ferbente molecule This would leave the name wolframite
for mixtures containing more than 20 per cent of both FcW04 and
MnW04
Analyses of specimens of hubnente (I), wolframite (II and III)
and ferbente (IV) follow
W03 FeO MnO CaO Other Total
I Ellsworth, Nye Co , Nev 7488 56 2387 .14 16 9961
II Sierra Cordoba, Argentine 7486 1345 ".°2 , 122 10055
III Cabarrus Co , N C . 7579 1980 5.35 .32 tr 101.26
IV, Kwnbosan, Japan 75 47 24 33 tr tr 99.80
All members of the group crystallize m the monoclinic system
(prismatic class) with axial ratios as follows
CHROMATES, TUNGSTATES AND MOLYBDATES 259
Ferbente a . b c= 8229 i
Wolframite = 8300 i
Ilubmtite =8315 i
8463 0=89° 38'
8678 0=89° 38'
8651 0=89° 38'
The crystals are pusmatic or cubic in habit and are bounded by
ooP(uo), ooPooJioo), and two 01 more of the following oP(ooi),
oo P .56 (oio), oo P2(2io), P oo (on), -]P 66 (To2), - JP 66 (102), -P(in),
- 2?2(i2i) and +2P oo (102) (Fig 149) The
angle iioAiio for ferbente = 78° 51', for wol
frcimite 79° 23', and foi hubnente 79° 29'
Twins are fairly common, with oo P 66 (100)
the twinning plane Cleavage is perfect
parallel to oo P 03 (oio) The minerals also
occur m lamellar and granular masses
Hubnente is brownish red to black and
translucent, wolframite is black and trans-
lucent only on thin edges, and ferbente is ^'49 -Wolframite Crys-
, . . / * ' . .. tal with oop, no (m),
black and opaque. The streak is yellow to oopj, 2io (/) oopoo
yellowish brown in hubnente and brown or 100(0), — JPoo, 102 (/),
brownish black in ferbente, with the streak P«, 011 (/), — 2Fa,iai
of wolframite between W> +ip55> i°* (y) and
Wolframite is buttle, has a hardness ot ~~P> IIX W
5-5 5, a specific gravity of 72-75, and a submetallic luster Before
the blowpipe it fuses to a globule which is magnetic Fused with
soda and niter on platinum it gives the bluish green manganate. The
salt of phosphorus bead is reddish yellow when hot and a paler tint
when cold. In the reducing flame the bead becomes dark red If
the mineral is treated first on charcoal with tin its bead assumes a
green color on cooling. The mineral dissolves in aqua regia with
the production of the yellow tungsten trioxide When treated with
concentrated HgSOi and zinc it yields the blue tungsten reaction
Crystals of wolfiamite are easily distinguished from crystallized
colnmbiie (p 293), samarskite (p. 295), and uraninite (p 297), by dif-
ferences in crystallization Massive wolframite is distinguished from
massive forms of the other three minerals by its more perfect cleavage
and by the reactions with the beads Uranmite, moreover, contains
lead Wolframite is distinguished from black tourmahne (p. 434) by
the differences m specific gravity,
Occurrence and Ongin — Wolframite usually occurs in veins with tin
ores, and in quartz veins with various sulphides, and in pegmatite.
Its origin is probably pneumatolytic.
260 DESCRIPTIVE MINERALOGY
Localities —Wolframite is found m all tm-producmg districts, espe-
cially at Zmnwald, Schneeberg and Freiberg, in Germany, at Ner-
chinsk, in Siberia, m Cornwall, England, at Oruro, in Bolivia, and at
various points in New South Wales, Australia
In the United States it occurs at Monroe, Conn , near Mine La
Motte, Missouri, near Lead, South Dakota, where it impregnates a
sandy dolomite, and at Hill City in the same State in quartz veins,
sometimes containing cassitente, in Boulder Co , Colorado, in veins
m granite (ferbente), neai Butte, Montana, in quaitz veins carry-
ing silver ores (hubnente), and the quartz-cassitcnte veins near Nome
and on Bonanza Creek, in Alaska, and in quarts veins at various
points in Washington, Idaho, California, Nevada, New Mexico and
Arizona At some of these localities the mineral is more properly
hubnente
One or another of the three has been mined in Colorado, Nevada,
South Dakota, Montana, Washington, Calif oinu, Aiizona, and New
Mexico, but the total production has never been laige Some of the
ore shipped has been obtained from placers along streams that dram
regions containing the mineral m veins, but most of it has been obtained
from vein rock which is crushed and concentrated
Uses — These three minerals constitute the principal source of tung-
sten used in the arts The uses of the metal are referred to under
scheehte
Production — The total production of concentrates containing 60
per cent WOs in the United States during 1913 was 1,325 tons, valued
at $640,500. Of this, 953 tons were ferberite from Boulder Co.,
Colorado A little hubnente was produced in the Arivica region, m
southeast California, at Dragoon, Arizona, at Round Mountain, Nevada,
and on Paterson Creek, Idaho. In addition, there were imported
$86,000 worth of tungsten-beaimg ores and $143,800 worth of tung-
sten metal and ferro-tungsten. The world's production of tungsten ore
in 1912 was 9,115 tons.
CHAPTER XIV
THE PHOSPHATES, ARSENATES AND VANADATES
THE phosphates are salts of phosphoric acid, HsPO^ the arsenates
of the corresponding arsenic acid, HsAsO^ and the vanadates of the
corresponding vanadic acid, HaVC^ The phosphates are by far the
most important as minerals They are easily distinguished by yielding
phosphme, HsP, upon igniting with metallic magnesium and moistening
the resulting Mg3P2 with H20 or HC1 (Mg3P2+6HCl=3MgCl2+
2PHs) The gas is recognized by its disagreeable odor The arsenates
are detected by the test for arsenic
The arsenates, phosphates and vanadates form groups of isomor-
phous compounds, the most important of which is the apatite group
Those occurring as minerals are divisible into several subgroups, of
which the following six contain common minerals, viz (i) anhydrous
(a) normal salts, (V) basic salts and (c) acid salts, and (2) hydrous
(a) normal salts, (b) basic salts and (c) acid salts
A number of the phosphates and arsenates are of value commercially
either because of the phosphorus they contain, because they are sources
of valuable metallic salts, because they serve to indicate the presence
of other valuable compounds, or because they possess an ornamental
character
Nearly ail the phosphates are transparent or translucent and all are
nonconductors of electricity or are very poor conductors,
ANHYDROUS PHOSPHATES, ARSENATES AND
VANADATES
NORMAL PHOSPHATES, ARSENATES AND VANADATES
The minerals belonging in this class of compounds are not as numer-
ous as the basic salts, but some of them are of great value The class
includes phosphates of yttrium, the alkalies, beryllium, cerium, mag-
nesium, iron and manganese and a group of isomorphous phosphates,
arsenates and vanadates— -the apatite group— in which a haloid radicle
replaces one of the hydrogen atoms of the acids Apatite, the prin-
cipal member of the group, is an important source of phosphoric acid
261
262 DESCRIPTIVE MINERALOGY
Triphylite— (Li(Mn Fe)PO4)— Littuophilite
Triphylite is the name usually applied to the isomorphous mixture
of LiFeP04 and LiMnP04, m \vhich the manganese molecule is present
in small quantity only The mixture containing a large excess of the
manganese molecule is called lithiophihte
The pure tnphyhte molecule contains FeO=45 5 Per cent, LigO
= 9 5 per cent and P2Ch=45 per cent The pure lithiophilite molecule
consists of 45 i per cent MnO, 9 6 per cent Li20 and 45 3 per cent
P205
Both substances are orthorhombic (bipyramidal class), with an axial
ratio approximating 4348 " i : 5265 Crystals are rare and not well
developed They are usually rough prisms bounded by ooFoo (oio),
oP(ooi), ooP(no), ooP2(i2o) and 2Po6 (021) The minerals usually
occur massive, or in irregular, rounded crystals, with two very dis-
tinct cleavages
Both minerals are transparent to translucent, both have a white
streak, and both are vitreous to resinous in lustci Thou baldness is
about 4 5-5 and sp gr about 3 5 Triphylite is greenish gray to blue,
and lithiophilite pink, yellow or brown The refi active indices for
light brown lithiophihte are a=i 676, j3=i 679, 7=1 687, those for
blue triphyhte are a trifle higher
When heated in closed tubes both compounds are apt to turn dark
They fuse at a low temperature (i 5) and color the flame crimson In
the case of tnphyhte the crimson streak is bordered by the green of iron.
Lithiophilite gives the reactions for Mn Most specimens give reac-
tions for all these metals — Fe, Mn and Li Both minerals are soluble
inHCl
The two minerals are distinguished from other compounds by their
reactions for phosphorus and lithium, and from each other by the reac-
tions for Fe and Mn
Occurrence — They usually occur as primary constituents of coarse
granite veins They are associated with beryl, tourmaline and other
pneumatolytic minerals and with secondary phosphates, which are
presumably weathering products of the pnmary phosphates
Locahties — Both minerals occur at a number of points associated
with other lithium compounds, especially spodumene (p 378) In this
country tnphylite has been found at Peru, Maine, Grafton, Ne\\
Hampshire, and Norwich, Massachusetts, lithiophihte at Branchville,
Connecticut, and at Norway, Maine
Neither of the minerals possesses a commercial value at present.
PHOSPHATES, ARSENATES AND VANADATES 263
Beryllonite (NaBeP04)
Beryllomte is a comparatively rare mineral occurring at only a few
places and al\\tiys in crystals or in crystalline grams
Its composition is 24 4 per cent Na^O, 19 7 per cent BeO and 55 9
per cent P2Cb
Its crystals are orthorhombic (bipyramidal class), with an axial
ratio 5724 • i * 540° They are short pyramidal or tabular in habit,
often exhibiting a pseudohexagonal symmetry. Most crystals are
highly modified with oP(ooi), oo P 60 (100), oo P 66 (oio), P 66 (101)
and 2P?(i2i), the principal forms Twins are common, with oo P(no)
the twinning plane The crystal faces are frequently strongly etched
The mineral is white to pale yellow It has a vitreous luster,
except on oP(ooi), where the luster is sometimes pearly It possesses
four cleavages, of which the most perfect is parallel to oP(ooi). That
parallel to oo P 60 (100) is distinct, but the others are indistinct Its
hardness is 5 5-6 and its density 2 845 Its fracture is conchoidal
Crystals often contain numerous inclusions of water and liquid C02
arranged in lines parallel to L Its refractive indices for yellow light
are a=i 5520, jS=i 5579, 7=1 5608
Beiyllomte decrepitates and fuses in the blowpipe flame to a cloudy
glass, at the same time imparting to the flame a yellow color It is
slowly soluble in HC1, and gives the phosphorus reaction with mag-
nesium
It is distinguished from most other colorless transparent minerals
by the reaction for phosphorus, from other colorless phosphates by its
crystallization and the sodium flame test
Occurrence and Localities — The best known occurrence of beryllo-
nite m the United States is Stoneham, Maine, where it is found in the
debris of a pegmatite dike associated with apatite (p 266), beryl (p. 359),
and other common constituents of pegmatites It originally existed
implanted on the walls of cavities in the pegmatite and was apparently
the result of pneumatolytic processes
Use. — The mineral is used to some extent as a gem stone,
Monazite ((Ce Di La)PO4)
Monazite is the principal source of certain rare earths that are used
m manufacturing gas mantles Although it occurs as small grams and
crystals m certain granites it is found m commercial quantities only m
the sands of streams.
264 DESCRIPTIVE MINERALOGY
The mineral is a phosphate of the metals cerium, lanthanum, praseo-
didymium and neodidymium in most cases combined with the silicate of
thorium Its composition may be represented by the formula
*((Cc La Di)P04)+^(ThSi04),
in which the proportion of the second constituent varies from a trace to
an amount yielding 20 per cent ThC>2 Since this is not constant in
quantity it is not to be regarded as an essential portion pf the com-
pound It is probable that in monazite we have to do with a solid
solution of cerium and thorium phosphates, thorium silicate and oxides
of the rare metals
Monazite is monochnic with a b : c= 9693 ' i : 9255 and 0=
76° 20' Crystals are usually prismatic with the pinacoids oo P 56 (100),
ooPob(oio), the prism ooP(no), the two domes — POO(IOI) and
+P66(ioY) and the pyramids -P(in) and +P(nT) They are
often flattened parallel to the orthopmacoid
(Fig 150) The angle 1 10 A iTo= 86° 34'
Their cleavage is perfect parallel to oP
The color of the mineral is gray, yellow, red-
dish, brown or green It is usually transpar-
ent or translucent and sometimes opaque It
is brittle, has a white streak, and a resmous
luster Its hardness is 5-5 5 and its sp gr
FIG. 150— Monazite Ciys- 4 7-5 3, varying with the proportion of thorium
tal with oo POO, ioo (a), nt The refractive indices for yellow
00 P. 110 (0Z), 00 ?2, , , 0 0
»o (,), oo P S, oxo (*), hSht are a=I 7938, 7 - t 8452.
-Poo, ioi (w), +Pco, The mineral is infusible Before the blow-
iol (x) and P, nI (») pipe it turns gray, and when moistened with
H2S04 it colors the flame bluish green It is
difficultly soluble in HC1 and HNOs Most specimens are strongly
radioactive
Synthesis — Crystals of monazite have not been prepared, but crys-
tals of cerium phosphate similar to those of monazite have been made
by heating to redness a mixture of cerium phosphate and cerium chloride
Occurrence and Ongvn — Monazite occurs as the constituent of cer-
tain granites and granitic schists in small crystals scattered among the
other components In this form it is a separation from the granitic
magma When the granites are broken down to sand by weathering
the monazite is freed and because of its specific gravity it concentrates
in stream channels
Localities — Although the mineral is fairly widespread in the rocks,
PHOSPHATES, ARSENATES AND VANADATES 265
it is concentrated into commercial deposits at only a few places. The
most important of these are in southeastern Brazil, in Norway, and in a
belt 20 to 30 miles wide and 150 miles long extending along the east side
of the Appalachian Mountains from North Carolina into South Carolina
The mineral has also been reported from many points in ten coun-
ties in Idaho Near Centerville it may be m sufficient quantity to be
of commercial importance
Preparation — Monazitg is separated from the valueless sand in
which it is found, by washing, and the residues thus resulting are further
concentrated by a magnetic process The commercial concentrates
produced in this way usually contain from 3 to 9 per cent ThCfe, and
their price varies accordingly
Production and Uses — Monazite is the chief source of thorium oxide
used in the manufacture of incandescent gas mantles Formerly it was
produced in large quantity in the Carohnas, the production m 1909
amounting to 542,000 Ib , valued at $65,032, and in 1905 to
1,352,418 Ib , valued at $163,908. All of this was manufactured into
the nitrate of thorium in this country and the amount made was
not sufficient to meet the domestic demand. Consequently, large quan-
tities of the nitrate were imported In 1910-11 mining of the mineral
m the Carohnas ceased and all the monazite needed has been imported
since then The imports of thorium nitrate for 1912 were 117,485 Ib ,
valued at $225,386 and of monazite, an amount valued at $47,334
Xenotime (YPO4)
Xenotime, though essentially an yttrium phosphate, usually contains
erbium and in some cases cerium.
It occurs in tetragonal crystals
and m rolled grains Its axid
ratio is i 6177 and ^e angle
in A ill =* 55° 30' Its crystals
are octahedral or prismatic and
are bounded by oo P(iio),P(m),
and in some cases by oo P oo (100)
and 2P oo (201) (Fig 151) Their
cleavage is perfect parallel to FIG 151 -Xenotime Crystals with OOP no
•n/ \ onT iv W» P II3C W» ^ ^P00* I°° W
ooP(no) The mineral is brown, v "
pink, gray or yellow Its streak is a pale shade of the same color.
It is opaque and brittle Its luster is vitreous or resinous, its hardness
4-5 and specific gravity 45 Its indices of refraction are: e=i8i,
w=i 72
266 DESCRIPTIVE MINERALOGY
Xenotime is infusible, insoluble in acids and with difficulty soluble
in molten microcosmic salt It is distinguished from zircon by its
cleavage and inferior hardness
A variety of xenotime containing a small percentage of sulphates is
known as hussakite
The mineral occurs in pegmatite veins, in granites and in the sands
of streams It is found in pegmatite veins at Hittero, Moss, and other
places in Norway, at Ytterby, Sweden, in the granites of Mmas Geraes,
Brazil, and m the gold washings at Clarksville, Georgia, and many places
in North Carolina, and in pegmatite veins in Alexander County in the
same State
APATITE GROUP
The apatite group consists of a number of phosphates, arsenates and
vanadates in which fluorine or chlorine takes the place of the hydroxyl
in basic compounds Thus, fluorapatite is Ca4(CaF)(P04)s and chlor-
apatite Ca^CaGXPOOs The group contains a number of important
minerals, of which apatite is by far the most valuable These minerals
are isomorphous, all crystallizing in the hemihedral division of the hex-
agonal system (hexagonal bipyramidal class) The names, composi-
tions and axial ratios of the most important are as follows
Fluorapatite Ca4(CaF)(PC>4)3 a c=i 7346
Chlorapatite Ca^CaClXPCWs a c**i: 7346+
PyromorpTtite Pb4(PbCl)(P04)3 a.c=i 7293
Mimetite Pb4(PbCl)(As04)3 0 . e-i : 7315
Vanadmite Pb4(PbCl)(V04)s a:c-i: 7122
Apatite (Ca4(Ca(F C1))(PO4)3)
Although fluorapatite and chlorapatite are distinct compounds with
slightly different properties, nevertheless, because of the difficulty of
discriminating between them without analyses, the name apatite is
commonly applied to both This is justified because of the fact that the
two compounds are completely isomorphous, and the mineral as it
usually occurs is a iruxture, of both The ideal molecules comprising
the two varieties of apatite have the following compositions
Fluorapatite CaO=5S5, F=3 8, P205=42 3
Chlorapatite CaO=53 8, Cl=6 8, P20s==4i o
Apatite is found in well defined crystals, sometimes very large
These have a holohedral habit, but etch figures on their basal planes
PHOSPHATES, ARSENATES AND VANADATES 267
reveal the grade of symmetry of pyramidal hemihednsm The min-
eral occurs also massive, in granular and fibrous aggregates and less
commonly in globular forms and as crusts
The crystals are usually columnar or tabular, with the hexagonal
prism or pyramid well developed Although in some cases highly
modified, most crystals contain only the oo P(iolo), P(ioTi) and oP(oooi)
planes prominent, though £P(iol2) and 2P2(ii2i) are not uncommon as
small faces (Figs 152 and 153) Their cleavage is indistinct, and their
fracture often conchoidal
Apatite may possess almost any color In a few cases the mineral is
colorless or amethystine and transparent, but in most cases it is trans-
lucent or opaque and white, green, bluish, brown or red Its streak is
FIG 152. FIG 153
FIG 152 — Apatite Crystals with cop, ioYo (w), P, loTi (r), oP, oooi (c), JP,
iol2 (r) and oop2, 1120 (a)
FIG 153 — Apatite Crystal with m, %, r and c as in Fig 152 and 2?, 2021 (y), 4P|,
1341 (»), 3?J, 1231 GU), 2P2, nil (5), P2, 1122 (B) and oo?}, 1230 (A)
white and its luster vitreous to resinous Its hardness is 4 5-5 and sp
gr between 3 09 and 3 39 The refractive indices of fluorapatite for
yellow light are 6>=i 6335, €=1.6316 and of chlorapatite, co=i 6667
Many specimens are distinctly phosphorescent Nearly all fluoresce in
yellowish green tints, and all are thermo-electric
Apatite fuses with difficulty, tinging the flame reddish yellow The
chlorapatite melts at 1530° and the fluorine variety at 1650° When
moistened with H2S04 all varieties color the flame pale bluish green,
due to the phosphoric acid Specimens containing chlorine give the
brilliant blue color to the flame when fused in a bead of microcosmic
salt that has been saturated with copper oxide Specimens containing
fluorine etch glass when fused with this salt in an open glass tube
The mineral also yields phosphme when ignited with magnesium, and
it dissolves in HC1 and HNOs
268 DESCRIPTIVE MINERALOGY
Apatite is much softer than beryl (p 359)> which it closely resembles
in appearance It is distinguished from calcite by lack of effervescence
•with acids and from other compounds by the phosphorus reaction
The vaneties of the mineral recognized by distinct names are
Ordinary apatite^ crystals or granular masses
Manganapatite, in which manganese partly replaces the Ca of ordi-
nary apatite^ This is dark bluish green
Fibrous, conci etionary apatite Known also as phosphorite
Osteohte The earthy variety
Phosphate rock. A mixture of apatite, phosphorite, several hydrous
carbonates and phosphates of calcium, and fragments of bone and
teeth It is more properly a rock with a brecciated and concretionary
structure The composition of typical deposits is represented by the
following analysis of hard rock phosphate from South Carolina
CaO P205 C02 Fe203 Al20s MgO Insol Undet H20 Moist
50 08 38 84 65 96 3 07 30 49 2 46 2 96 07
Guano is a mixture of various phosphates, both hydrous and an-
hydrous, calcite and a number of other compounds It is rather a rock
than a mineral, as it has no definite composition
Syntheses —Crystals of fluorapatite have been made by fusing
sodium phosphate with CaF2 and by heating calcium phosphate with a
mixture of KF and KC1
Origin — The crystallized apatite was formed by direct separation
from igneous rock magmas and by pneumatolytic action upon limestone
The phosphorite variety and the phosphate in phosphate rock were
probably produced by the solution of calcium phosphate and its later
deposition from solution— the original phosphate having been furnished
in many cases by the shells of mollusca, and by the action of phosphoric
acid produced by the decay of organisms upon limestone In many
cases phosphorite accumulated as a residual deposit in consequence of
the solution of the calcite and dolomite from phosphatic limestone,
leaving the less soluble phosphate as a mantle on the surface.
Occurrence — The mineral occurs in microscopic crystals as a com-
ponent of many rocks, as large crystals in metamorphosed limestones,
as a component of many coarse-grained veins, especially those composed
of coarse granite and those in which cassiterite, magnetite, tourmaline,
and other pneumatolytic minerals are found At a number of places
aggregates of apatite and magnetite or ilmemte occur in such large
masses as to be worthy of being called rocks An impure apatite in
concretionary and fibrous forms also occurs in thin beds covering large
PHOSPHATES, ARSENATES AND VANADATES 269
areas. It is often mixed with other phosphates, with the bones and
teeth of animals and with other impurities This is the well known
phosphate rock or phosphonte
Localities — Crystallized apatite is so widely spread that it is useless
to mention its occurrences It is mined at Kragero and near Bamle,
in Norway, at various points in Ottawa County in Quebec, and in
Frontenac, Lanark and Leeds Counties in Ontario, and at Mineville,
New York Rock phosphate is found in extensive beds on the west
side of the peninsula of Florida, in South Carolina, North Carolina,
Alabama, Tennessee, Wyoming, Idaho, Utah and Arkansas A mixture
of apatite and ilmemte (nelsomte), occurs as dikes in Nelson and
Roanoke Counties, Virginia
Uses — The principal use of apatite and phosphate rock is in the
manufacture of fertilizers The rock (or crushed apatite) is treated
with H2S04 to make an acid phosphate which is soluble in water Am-
monia or potash, or both, are added to the mass and the compound is
sold as a superphosphate. The purest varieties are treated with H2S04
in sufficient quantity to entirely decompose them, CaSO* and HsPO*
being formed The latter is drawn off and mixed with additional high-
grade rock and the mixture is known as concentrated phosphate Super-
phosphates are manufactured in large quantities in the United States
and the concentrated phosphates in Europe Unfortunately, for the
latter use the best grades of apatite or rock phosphate are required, and
consequently the best grades of rock produced in the United States are
exported and thus lost to American farmers
Production —The world's production of apatite and phosphate rock
during 1912 was as follows*
United States 3,020,905 tons, valued at $11,675,774
Tunis 2,050,200 tons, valued at 7,500,000
Christmas Island 159459 tons, valued at 2,024,036
France 313*151 tons, valued at 1,169,400
Algeria 207,111 tons, valued at 759455
Belgium 203,1 10 tons, valued at 316,703
Other countries 65,000 tons, valued at 280,000
For the United States production of 1912 the statistics are:
Florida 2,407,000 tons, valued at $9,461,000
Tennessee 423,300 tons, valued at 1,640,500
South Carolina 131,500 tons, valued at 524,700
Other States 11,600 tons, valued at 49»200
270 DESCRIPTIVE MINERALOGY
The total production was 3,020,905 tons, valued at $11,675,77400,
of which 1,206,520 tons, valued at $8,996,45600 were exported Par-
tially offsetting this, there were imported guano, apatite and other phos-
phates to the value of about $2,000 ooo,
Pyromorphite (Pb4(PbCl)(PO4)3)
In composition pyromorphite is PbO, 82 2 per cent, PoO«i, 15 7 per
cent and Cl, 2 6 per cent, but there are usually present also CaO and
The mineral is completely isomorphous \\ith apatite Its crystals
are smaller and simpler than those of apatite, but they have the same
habit Their axial ratio is a c=i ' 7293 This increases to i : 7354
in varieties containing calcium
Crystals are often rounded into barrel-shaped forms, and frequently
are mere skeletons Tapering groups of slender crystals in parallel
growths are also common Their cleavage is parallel to the &o P(no)
faces, and their fracture is feebly conchoidal. The mineral also occurs
in globular, granular and fibrous masses
Pyromorphite is translucent It is brittle, has a hardness of 3 5-4
and a density of about 7 Its luster is resinous and color usually green,
yellow, brown or orange Some varieties are gray or milk-white Its
streak is white Its refractive indices foi yellow light are: o>=2 0614,
6=2 0494 The mineral is distinctly thermo-electric.
When heated m the closed tube pyromorphite gives a white subli-
mate of lead chloride It fuses easily, coloring the flame bluish green
When heated on charcoal it melts to a globule, which crystallizes on
cooling and yields a coating which is yellow (PbO) near the assay and
white (PbCk), at a greater distance from it. When fused with Na2COs
on charcoal a globule of lead results The mineral also gives the Cl and
P reactions The mineral is soluble in HNOa
Pyromorphite is recognized by its form, high specific gravity and its
action when heated on charcoal
Synthesis. — Crystals have been obtained by fusing sodium phosphate
with PbCk.
Occurrence— The mineral occurs principally m veins with other lead
ores, especially in the zone of weathering It also exists in pseudomorphs
after galena.
Localities — It is found in all lead-producing regions, especially in
the upper portions of veins It occurs m particularly good specimens
at Pribram, Bohemia, at Ems, m Nassau, in Cornwall, Devon, Derby-
PHOSPHATES, ARSENATES AND VANADATES 271
shire and Cumberland, England, at Phoemwille, Pennsylvania, and
at various other points in the Appalachian region
Vies— Pyromorphite alone possesses no commercial value, but it
is mined with other compounds of lead as an ore of this metal
Munetite (Pb4(PbCl)(AsO4)3)
Mimetite, or mimetesite, resembles pyromorphite in its crystals and
general appearance, and many of its properties Its color, however, is
lighter and its density slightly greater It occurs in crystals, m fila-
ments, and in concretionary masses and crusts Its axial ratio Is
i 7315 and its refractive indices for yellow light are w=2 1443, e
= 2 1286
The formula for mimetite demands 74 9 per cent PbO, 23 2 per cent
AS205 and 2 4 Cl Usually a portion of the lead is replaced by CaO and
a portion of the As by P
Mimetite fuses more easily than pyromorphite It differs from this
mineral in yielding arsenical fumes when heated on charcoal More-
over, when heated in a closed tube with a fragment of charcoal it coats
the walls of the tube with metallic arsenic
Occurrence and Localities — It occurs with other lead minerals in
veins, usually coating them either as crusts or as a series of small crys-
tals It is found at Phoenix ville, Pennsylvania, m Cornwall, England,
at Johanngeorgenstadt, in Germany, at Nerchinsk, Siberia, at Lang-
ban, in Sweden, and at a number of other places It is, however, not
as common as the corresponding phosphorus compound
Uses — It is mined with other compounds as an ore of lead.
Vanadiaite (Pb4(PbCl)(VO4))3
Vanadmite is the most widely distributed of all the vanadium min-
erals It usually occurs in small bright red prismatic crystals implanted
on other minerals, or on the walls of crevices in rocks It is one of the
sources of vanadium
Its theoretical composition is as follows PbO =78 7 per cent,
¥205=19 4 per cent and Cl=2 5 per cent, but phosphorus and arsenic
are often also present When arsenic and vanadium are present m
nearly equal quantities the mineral is known as endhckite.
Its crystals are hexagonal prisms and pyramids bounded by
ooP(ioTo), oP(oooi), ooP2(u5o\ P(ioTi) and other forms, with an
axial ratio i : .7122 (Fig 154). Often the crystals have hollow faces
272
DESCRIPTIVE MINERALOGY
(Fig IS5) Frequently they are grouped into pyramids like those of
pyromorphite The mineral occurs also m globules and crusts
Vanadmite is brittle, has a hardness of about 3 and a specific gravity
of about 7 Its fracture is conchoidal Its luster is adamantine or
resinous and its color ruby red, brownish yellow or reddish brown
Its streak is white or light yellow The mineral is translucent
or opaque Its refractive indices for yellow light are ^=2354,
€= 2 299
In the closed tube vanadimte decrepitates It fuses easily on char-
coal to a black lustrous mass which is reduced on being further heated
in the reducing flame to a globule of lead A white sublimate of PbCk
also coats the charcoal The mineral, moreover, gives the flame test
FIG. 154
FIG 154 FIG 155
—Vanadimte Crystal with <x>p, loTo (m), oP, oooi (c), P, icTi (#), and
FIG 155 — Skeleton Crystal of Vanadimte
for chlorine with copper After complete oxidation of the lead by heat-
ing in the oxidizing flame on charcoal the residue gives an emerald-green
bead in the reducing flame with microcosmic salt and this turns to a
light yellow m the oxidizing flame The mineral is soluble m hydro-
chloric acid. If to the solution a little hydrogen peroxide is added it
will turn brown The addition of metallic tin to this will cause it to
turn blue, green and lavender in succession, in consequence of the reduc-
tion of the vanadium compounds
Vanadimte is easily distinguished from most other minerals by its
color, It is distinguished from other compounds of the same color by
its crystallization and by the reactions for vanadium
Occurrence — Vanadmlte occurs principally in regions of volcanic
rocks It is probably a result of pneumatolytic processes
Localities —Crystals are found at Zimapan, Mexico, Wanlockhead,
PHOSPHATES, ARSENATES AND VANADATES 273
England, Undenas, Sweden, in the Sierra de Cordoba, Argentine, and in
the mining districts of Arizona and New Mexico
Uses — Vanadmite is an important source of vanadium, which is
employed m the manufacture of certain grades of steel and bronze
Its compounds are, moreover, used as pigments and mordants Most
of the vanadium compounds produced in this country are obtained from
other vanadium minerals, among them patromte — a mixture, of which
the principal component is a sulphide (VS.*) — and carnotite (p 290),
but vanadmite has been used abroad and also to a small extent in the
United States
WAGNERITE GROUP
This group, in chemical composition, is analogous to the apatite
group It includes a number of phosphates and arsenates containing a
fluoride radical The group is monochmc (prismatic class), with an
axial ratio which is approximately 19.1 15, with 18=71° 50' None
of its members are important The two most common ones are wag-
nente (Mg(MgF)PO4), and tnphte (Fe Mn) ((Fe Mn)F)P04
Wagnerite occurs in massive forms and in large rough crystals, with
imperfect cleavages parallel to oo P 55 (100) and oo P(no) Its crystals
have an axial ratio of i 9145 • i . i 5059 \vith £=71° 53' They are
often very complex The mineral is bnttle Its fracture is uneven
Its hardness is 5 5 and density 3 09 Its color is yellow, gray, pink or
green It is vitreous, translucent and has a white streak Its refractive
indices are a=i 569, £=i 570, 7 = 1 582 It fuses to a greenish gray
glass and gives the usual reactions for fluorine and phosphoric acid It
is soluble in HC1 and HNOa, and heated with HgSOi it yields hydro-
fluoric acid It occurs in good crystals near Werfen, Austria, and in
coarse crystals near Bamle, Norway.
Triplite is an isomorphous mixture of Fe(FeF)PO4 and Mn(MnF)P04
It usually occurs massive, but is found in a few places in rough crystals
The mineral is dark brown or nearly black, is translucent to opaque,
and has a yellowish gra}' or brown streak It possesses two unequal
cleavages perpendicular to one another and a weakly conchoidal frac-
ture Its hardness is 4-5 5 and specific gravity about 3 9 Its luster is
resinous. Its intermediate refractive index is i 660
Before the blowpipe tnplite fuses easily (i 5) to a black magnetic
globule It reacts for Mn, Fe, F, and PaOs It is soluble in HC1 and
evolves hydrofluoric acid with H2S04 It is found in coarse granite
274 DESCRIPTIVE MINERALOGY
veins at Limoges, France, Helsingfors, Finland, Stoneham, Maine,
and Branchville, Connecticut In all of its occurrences it appears to
be pneumatolytic
BASIC PHOSPHATES AND ARSENATES
The basic phosphates are those in which there is more metal present
than sufficient to replace the three hydrogen atoms in the normal acid,
HsP04 This is due to the replacement of one or more of the hydrogen
atoms by a group of atoms consisting of a metal and hydroxyl (OH)
All yield water when heated in the closed tube
The principal basic phosphates are amblygonite, a source of lithium
compounds, dufremte and lazidite, neither of which is of economic im-
portance, and hbethemte, a copper compound which occurs in compara-
tively small quantities with other copper ores, and is mined with
them
Ohvenite is a basic copper arsenate corresponding to the phosphate
hbethemte
Amblygonite (Li(Al(F OH))PO4)
Amblygomte is an isomorphous mixture of the two compounds
(AlF)LiP04 and (AlOH)LiPO-i It is an important source of lithium
The composition of the fluorine molecule is Al20s=344 per cent,
Li02=io i per cent and P20s=47 9 per cent, making a total of 105 3
per cent from which deducting 5 3 per cent (0= sF), leaves 100 Nearly
always a portion of the F is replaced by OH and a part of the Li
by Na The pure Na(A10H)P04 is known as fremontite, and the pure
Li(A10H)PO4 as montebrmte
The analysis of a specimen from Pala, California, gave:
Pa06 AlsOs PesOs MnO MgO LiaO NaaO H8O 0-P Total
4883 3370 12 09 31 988 14 595 229*10131-96 - 100 45
The mineral forms large, ill-defined triclmic crystals (Fig 156), and
compact masses with a columnar cleavage Crystals are very rare, and
are poorly developed Their axial ratio is .7334 : i : 7633. The
cleavage pieces often show polysynthetic twinning lamellae parallel to
The cleavage of the mineral is perfect parallel to oP(ooi) Its
fracture is uneven It is brittle, has a hardness of 6 and a density of
3 03, Its color is white, gray, or a very light tint of blue, pink or
yellow Its luster is vitreous, except on oP where it is pearly. ' Its
PHOSPHATES, ARSENATES AND VANADATES 275
FIG 156 — Amblygoiute
Crystal with ooPoo,
100 (a), oP, ooi (c),
oo ]P, no (A/), °oP',
no (m)y w'P's, 120
(=), /P/J5, ioi (K)
and 2'P oo , 02 1 (e)
streak is white and it is translucent Its refractive indices for yellow
light are a=i 579, /3=i 593, 7=1 597
In the closed tube at high temperature it yields water which reacts
acid and corrodes glass It fuses easily to an
opaque white enamel It colors the flame red
with a slight fringe of green When moistened
with H2S04 it tinges the flame bluish green
When finely powdered it dissolves readily in
H2SO4 and with difficulty in HC1
Amblygomte resembles in appearance many
other minerals, especially spodumene (p 378),
and some forms of bante, feldspar, dolomite, etc
From spodumene it is distinguished by the phos-
phorus reaction and the acid water, from the
others by its easy fusibility
Occurrence — Amblygomte is found in granite
and in pegmatite veins associated with other
lithium compounds, tourmaline, cassitente and
other minerals of pneumatolytic origin In all cases it also is probably
a result of pneumatolytic action associated with the last phases of granite
intrusions
Localities — The mineral occurs near Pemg, in Saxony, at Arendal,
in Norway, at Montebras, France, at Hebron, Paris and Peru, Maine,
at Branchville, Conn , at Pala, m California, and near Keystone, in
the Black Hills, South Dakota
Uses and Production — The mineral is the pnncipal source of lithium
compounds in the United States. It is used in the manufacture of
LiCOa, which is employed as a medicine, in making mineral waters, in
photography and in pyrotechnics
It has been mined m South Dakota and in California to the extent
of a couple of thousand tons, valued perhaps at $20,000.
Dufrenite QfeaCOHJsPO*)
Dufreiute, or kraunte, is a basic iron phosphate containing 62 per
cent FegOs, 27 5 per cent P20s and 10 5 per cent water It may be
regarded as a normal phosphate in which one H atom of HsP04 has been
replaced by the Fe(OH)2 group and two by the group Fe(OH), thus
It forms small orthorhombic crystals with a cubic habit that are rare
Their axial ratio is .3734 • i • .4262. It usually occurs massive, in
276
DESCRIPTIVE MINERALOGY
nodules, or in fibrous radiating aggregates The same substance is
belie\ ed to occur also in the colloidal condition under the name ddvauute
The color of dufremte varies from leek-green to dark green, which
alters on exposure to yellow and brown It is translucent to opaque,
has a light green streak and is strongly pleochroic Its hardness is
3 5-4 and specific gravity about 3 3
In the closed tube it yields water and whitens It fuses easily, color-
ing the flame bluish green and yielding a magnetic globule It is sol-
uble in HC1 and in dilute H2S04
It is recognized by its color and the presence in it of water, phos-
phorus and iron
Localities and Origin — The mineral has been observed at several
points in Europe, at Allentown, New Jersey, and in Rockbridge County,
Virginia It is thought to be produced by the weathering of other fer-
ruginous phosphates
LazuHte ((Mg Fe)(AlOH)2(PO4)2)
Lazulite is essentially an isomorphous mixture of the two com-
pounds Mg(A10H)2(P04)2 and Fe(AlOH)2(POi)2 There is also fre-
quently present m it a little calcium
When the proportion of the two
molecules present is as 2 . i the com-
position becomes FeO = 77, MgO
= 85, A1203 = 32 6, P205 = 4S 4 and
H20=S8
The mineral occurs m blue pyram-
idal crystals that are monoclimc
(prismatic class), with the axial ratio
= 9750 • i • i 6483 and 0=89° 14'
The predominant forms are +P(nT),
FIG 157— Lazulite Crystals A with — P(lli) and— P 56 (ioi)(Flg 157-4)
-P, in (p) H-P, nl (e) and P 65 , xhe angle in A if i = 79° 40' Twins
ioi (/) B is the same combination
twinned about oo p oo (100) with oP
(ooi) the composition face
are not common Those most fre-
quently found are twinned about c
as the twinning axis (Fig 1576)
It is found also massive and in granular aggregates
The cleavage of lazuhte is not distinct Its fracture is uneven It
is brittle, has a vitreous luster, is translucent or opaque, has an azure
color and a white streak Its hardness is 5 or 6 and its specific gravity
about 3 i Translucent crystals are strongly pleochroic in deep blue
and greenish blue tints — the former when viewed along the vertical
PHOSPHATES, ARSENATES AND VANADATES 277
axis Their indices of refraction for yellow light are a= i 603, /?= i 632,
7=i 639
In the closed tube lazuhte swells, whitens and yields water When
heated in the blowpipe flame it whitens, falls to pieces and colors the
flame bluish green The white powder moistened with Co(NOs)2 and
reheated regains its blue color. When moistened with HgSC^ and
heated in the blowpipe flame it imparts to it a green blue color It is
infusible and is unacted upon by acids
Lazulite, when massive, closely resembles in appearance massive
forms of some varieties of sodahte, hauymte and lazunte (p 333) The
latter, however, are soluble in HC1. Moreover, none of them contains
phosphorus
Occurrence — The mineral occurs in quartz veins in sandstones and
slates and is usually a product of metamorphism It is sometimes, how-
ever, found in serpentine rocks, with corundum, in which case it may be
original
Localities — Good crystals occur at Kneglach, in Styna, at Horrs-
joberg, in Sweden, and in the United States at Crowder's Mountain,
North Carolina, and on Graves Mountain m Georgia,
OLIVENITE GROUP
The ohvenite group includes a number of basic copper, lead and
zinc compounds of the general formula R"o(OH)R'"04 m which R"
= Cu, Zn, Pb and R'"=As, P, V The group is
orthorhombic (bipyramidal class), with axial ratios
approximating 95 . i 70 The most important
members of the group are the two copper min-
erals, ohvemte, Cu(CuOH) As04 and libethemte,
Cu(CuOH)P04
Ohvenite occurs m fibrous, globular, lamellar,
granular and earthy masses and in prismatic and
acicular crystals bounded by oo P(uo), oo P 60 (100),
oo P 06 (oio), P & (on) and P 56 (101) (Fig 158)
Their axial ratio is 9396 i . 6726 and the angle
1 10 A 1 10= 86° 26'. Their cleavage is poor.
The mineral is some shade of green, brown,
yellow or grayish white and its streak is olive-green
m greenish varieties. It is transparent to opaque, is brittle, has a
hardness=3, and a specific gravity =4.3. Its refractive indices for
to 158 — Ohvenite
Crystal with oo Poo,
zoo (a), oo p, no
(m), oo Poo ,010 (6),
P oo , on (e) and
P 55 , 101 (»)
278 DESCRIPTIVE MINERALOGY
ydlow light are about i 83. Its luster is usually vitreous Fibrous
vaneties are sometimes known as wood-copper
Ohvemte fuses easily (2) to a mass that appears crystalline on cooling
It gives the usual reactions for EkO, Cu, and As It is soluble in acids
and in ammonia
It is associated with other copper compounds in some copper ores
Its ongin is secondary in all cases It occurs in the Tmtic district,
Utah, and in many copper veins in Europe and in South America
Libethenite occurs in compact or globular masses and in small
crystals that resemble those of ohvemte Their axial ratio is 9605 :
i 7019 and no A 110=87° 40'
The mineral is bnttle Its fracture is indistinctly conchoidal Its
color is dark ohve-green and its streak a lighter shade It is translucent
or transparent and has a resinous luster Its hardness =4 and sp gr
=37. Its intermediate refractive index for yellow light is i 743
When heated in the closed tube it yields water and blackens It is
easily fusible (2) It yields the usual reaction for Cu and P, and is sol-
uble m acids and in ammonia It is distinguished from ohvemte by the
reaction for phosphorus
It occurs at many of the localities for ohvemte, where, like this min-
eral, it is a decomposition product of other copper compounds.
Eerderite (CaBe(OH'F)P04)
Herdente is an isomorphous mixture of the two phosphates, CaBeFP04
and CaBe(OH)P04. The latter molecule occurs in nature as hydro-
kerdente, the former occurs only in mixtures The theoretical compo-
sition of the fluorine (I) and bydroxyl (II) molecules and of transparent
crystals from Stoneham (III), and Pans (IV), Maine, are given below
BeO CuO P205 F H20 Ins.
. . . 100
5 59 - ioo
3 70 99 67
44 ioo 51
The mineral is found only in crystals, which are monoclmic, with
a : b : $=.6301 : i : .4274 and £=89° $4*. Their habit is hexagonal,
pyramidal or short prismatic, elongated in the direction of a
I- IS 39
34 33
43 53
ii 64
II. 15 53
34 78
44 10
III. 15 51
33 67
43 74
5 27
rv. 16 13
34 04
44 OS
53S
PHOSPHATES, ARSENATES AND VANADATES 279
Herdente is colorless or light yellow, transparent or translucent
Its refractive indices are a= i 592, /3= i 612, y= i 621
Its density is about 3, diminishing, as the amount of hydroxyl in-
creases, to 2 952 in the pure hydroherderite
Before the blowpipe herderite first phosphoresces with an orange-
yellow light, then fuses to a white enamel, colors the flame red and yields
fluorine In the closed glass tube most specimens yield an acid water,
which, when strongly heated, evolves fluorine that etches the glass
The mineral also reacts for phosphorus with magnesium nbbon It is
slowly soluble in HC1
Occurrence^ Origin and Uses — Herderite occurs m pegmatite dikes
at Stoneham, Hebron, and other places in Maine, and at the tin mines of
Ehrenfriedersdorf, Saxony, in all of these places it is apparently of
pneumatolytic origin The material from Maine is used to a small
extent as a gem stone
ACID PHOSPHATES
Acid phosphates are those m which all of the hydrogen atoms of the
acids have not been replaced by metals or by basic radicals Theoret-
ically, they contain replaceable hydrogen atoms There are 12 or 15
minerals that are thought to belong to this class, but the composition
of many of them is very obscure Most of them appear to be hydrated
The only important mineral that may belong to the class is the popular
gem stone, turquoise. This, according to the best analyses, contains its
components in the proportions indicated by the formula CuO, 3Al2Os,
2P2Os, 9H20, which may be interpreted as (CuOH)(Al(OH)2)6H5(P04)4,
which is 4(HsP(>4), in which 6 hydrogen atoms are replaced by 6Al(OH)s
groups and one by the group CuOH.
Turquoise ((CuOH)(Al(OH)2)6H5(P04)4)
Turquoise is apparently a definite compound of the formula indicated
above, which requires 34 12 per cent P20s, 36 84 per cent Al20a, 9 57
per cent CuO and 19 47 per cent H20 Analysis of a crystallized variety
from Lynch, Campbell Co , Virginia, gave
P205 A1203 Fe203 CuO H20 Total
34 13 36 5° 2I 9 °° 20 I2 99 96
Most specimens, however, have not as simple a composition as this
They are probably isomorphous mixtures of unidentified phosphates.
280 DESCRIPTIVE MINERALOGY
The mineral as usually found is apparently an amorphous or cryp-
tocrystalline, translucent or opaque material with a wa\y lustei and a
sky-blue, green or greenish gray color Material recently found at
Lynch, Virginia, however, occurs in minute tnclmic crystals with an
axial ratio 7910 . i 6051, \Mtha=87°o2/?/3=86° 2q', and 7= 72° 19'
Their habit is pyramidal with ooP 60(100), oop 06(010), oo 'P(iTo),
ooP'(no) and POO (oil)
The fracture of turquoise is conchoidal. It has a hardness of 5-6
and a specific gravity between 261 and 2 89 It is brittle, and has cleav-
ages in two directions. The determined refractive indices of the Vir-
ginia crystals are: a=i.6i, 7= 1.65
In the closed tube the mineral decrepitates, yields water and turns
black or brown It is infusible, but it assumes a glassy appearance when
heated before the blowpipe and colors the flame green. When moistened
with HC1 and again heated the flame is tinged with the azure blue of
copper chloride The mineral reacts for copper and phosphoric acid
Some specimens dissolve m HC1, but the crystallized material from Vir-
ginia is insoluble until after it is strongly ignited It partly dissolves
in KOH, with the production of a brown residue of a copper compound
Occurrence — Turquoise occurs in thin veins cutting through certain
decomposed volcanic rocks and other rocks in contact with them,
and in grains disseminated through them, in stalactites, globular
masses and crusts It is probably an alteration product of other com-
pounds
Localities — Turquoise is found in narrow veins and irregular masses
in the brecciated portions of acid volcanic rocks and the surrounding clay
slates, near Nish&pur, in Persia, in the Megara Valley, Sinai, and near
Samarkand, in Turkestan In all these places the mineral is of gem
quality and until recently nearly all the gem turquoise came from them
Within late years gem turquoise has been discovered in the Cenllo Moun-
tains, near Santa Fe, New Mexico, where it has been mined in consid-
erable quantity The locality is the site of an ancient mine which was
worked by the Mexicans It is also found and mined in the Burro
Mountains, Grant County, in the same State, near Millers, and at other
points in Nevada and near Mineral Park, Mohave County, Arizona,
where also the ancient Mexicans once had mines At La Jara, Conejos
County, Colorado, old mines have likewise been opened up and are now
yielding gem material
Uses —The only use of turquoise is as a gem stone Though much
of the American mineral is pale or green, some of it is of as fine color as
the Oriental stone A favorite method of using the stone is in its
PHOSPHATES, ARSENATES AND VANADATES 281
matrix Small pieces of the rock with its included turquoise are pol-
ished and sold under the name of turquoise matrix
Production — The total value of the turquoise and turquoise matrix
produced in the United States during 1911 was $44,751 This weighed
about 4,363 pounds In several previous years the production reached
about $150,000, but in 1912 it was valued at only $10,140
HYDROUS PHOSPHATES AND ARSENATES
HYDRATED NORMAL PHOSPHATES AND ARSENATES
Of the hydrous salts of orthophosphonc and orthoarsemc acids there
are two which are of some importance because they are fairly common,
a third which is utilized in jewelry, and a fourth that is important as an
indicator of the presence of an ore of cobalt. The first two are wwanite
and scorodtte, a phosphate and an arsenate of iron, the third is vanszite,
an aluminium phosphate, and the fourth is erytknte, an arsenate of
cobalt A dimorph of vanscite, known as lucmite, is rare All give
water in the closed tube and yield phosphine when fused with magne-
sium and moistened with water
VIVIANITE GROUP
The only important group of the hydrated orthophosphates and
orthoarsenates is that of which viviamte and erythnte are members.
The general formula of the group is R"3(R'"04)2 8H20 in which R"
=Fe, Co Ni, Zn and Mg, and R'"=P or As Although some members
have not been found in measurable crystals, crystals of all have been
made in the laboratory, so that there is little doubt of their isomorphism.
All are monochmc prismatic with axial ratios of about 75 • i : 70 and
ft about 74° The group is as follows
Bob^ente, Mg3(P04)2 8H20 ErytMte, Co3(As04)2 8H20
Hornes^te, Mg3(As04)2 8H20 Annabcrgde, Nm(As04)2 8H20
Vtwamte, Fe3(P04)2 8H20 Cabrente, (Ni Mg)3(As04)2 8H2O
Symplestte, Fe3(As04)2 8H20 Kottigite, Zn3(As04)2 8H20
Only vivianite, erythnte and annabergite are described
Vivianite (Fe3(P04)2 8H2O)
Vivianite is a common phosphate of iron It occurs not only in dis-
tinct crystals but also as bluish green stains on other minerals, and as
an invisible constituent of certain iron ores, thereby diminishing their
value.
282 DESCRIPTIVE MINERALOGY
Its formula indicates the presence of 43 per cent FeO, 28 3 per cent
P20s and 28 7 per cent BkO
Viviamte crystals are monoclmic (prismatic class), usually with a
prismatic habit Their axial ratio is 7498 . i 7015, and £=75° 34'
The principal forms observed on them are oo P 56 (100), oo P ob (oio),
ooP(no), °oP3(3io), P&O(IOI), P(III) and oP(ooi) The angle
uoAi"io=7i° 58' The mineral also occurs in stellate groups, in glob-
ular, fibrous and earthy masses and as crusts coating other compounds
Its cleavage is perfect parallel to oo P «D (oio) It is flexible in
thin splinters and sectile. The fresh, pure mineral is colorless and trans-
parent, but specimens usually seen are more or less oxidized and have
a blue or green color It has a vitreous to pearly luster Its streak is
white or bluish, changing to indigo-blue or brown on exposure to the air
Its pleochroism is strong in blue and pale yellow tints Its hardness
is i 5-2 and density about 2 6. Its refractive indices for yellow light
are a=i 5818, jS-i 6012, 7-1 6360
In the closed tube viviamte whitens, exfoliates and yields water at a
low temperature It fuses easily (2), tingemg the flame bluish green
Its fusion temperature is 1114°. The fused mass forms a grayish black
magnetic globule. It gives the reaction for iron, and is soluble in HC1
The mineral is easily recognized by its softness, easy fusibility and
by yielding the test for phosphorus.
Synthesis — Crystals have been made by heating iron phosphate with
a great excess of sodium phosphate for eight days
Occurrence and Origin. — Vivianite occurs in veins of copper, tin and
gold ores; disseminated through peat, clay, and limomtc, coating the
walls of clefts in feldspars and other minerals of certain igneous rocks,
and partially filling cavities in fossils and partly fossilized bones It is
usually the result of the decomposition of other minerals
Localities, — Crystals are found at several points m Cornwall, Eng-
land, at the gold mines at Verespatak, in Transylvania, at Allentown,
Monmouth County, New Jersey, and at many other places The earthy
variety occurs at Allentown, Mullica Hill and other points in New Jer-
sey, in Stafford County, Virginia, and in swamp deposits at many places
It is abundant in limomte at Vaudreuil, in Quebec, and in bog iron ores
elsewhere.
Erythrite (Co3(As04)2 8H20)
Erythnte, or cobalt bloom, isinot a common mineral, but, because
of its beauty and the fact that it is the usual alteration product of cobalt
ores, it deserves to be described
PHOSPHATES, ARSENATES AND VANADATES 283
In composition erythnte is 37 5 per cent CoO, 38 4 per cent As205,
and 24 i per cent H20 It usually, ho\\e\er, contains some iron, nickel
and calcium
The mineral is isomorphous with vivianite Its crystals are mono-
climc and prismatic or acicular and their axial ratio is 7037 i • 7356
and jS=74° 51' The pnsms are stnated vertically Erythrite occurs
in all the forms in which vivianite is found Its crystals are usually
bounded by ooP 03(010), ooP(no), oop 66(100), +Po6(Toi) and
The cleavage of erythnte is perfect parallel to oo P ob (oio) It is
transparent or translucent, has a gray, crimson or peach-red color,
and a white or pink streak Its hardness varies between i 5 and 2 5
and its density is 295 Its luster is pearly on oo Poo (oio) and
vitreous on other faces It is flexible and sectile. Its refractive
indices for yellow light are a— i 6263, 0= i 6614, 7= i 6986
In the closed tube ery thrite turns blue and yields water at a low tem-
perature At a high temperature it yields As20<j, which condenses in
the cold portion of the tube as a dark sublimate It fises at 2, and
tinges the flame pale blue On charcoal it fuses, yields arsenic fumes and
a gray globule which colors the borax bead a deep blue The mineral
is soluble in HC1, giving rise to a pink solution, which, upon evaporation
to drynesSj gives a blue stain
It is easily recognized by its color and the cobalt reaction. It is
readily distinguished from pink tounna\ne (p 434), by its hardness
and easy fusibility
Synthesis — Crystals have been obtained by carefully mixing to-
gether warm solutions of CoSO-i and HNa2As04 7HsO
Occurrence — Erythnte occurs in the upper portions of veins con-
taining cobalt minerals, being formed by their weathering
Localities — Tt occurs as scales and crystals at Schneeberg, Saxony,
and as crystals at Modum, Norway. It is found, also, at Lovelock's
Station, Nevada, at several points m California and in large quantities
at Cobalt, Ontario.
Annabergite (Ni3(As04)2-8H20)
Annabergite, or nickel bloom, is isomorphous with erythnte It
occurs massive, disseminated m tiny grains through certain rocks, as
crusts and stains m globular and earthy masses, and in fibrous crystals,
the axial ratios of which are not known.
The mineral is apple-green in color, and is translucent or opaque.
284 DESCRIPTIVE MINERALOGY
Its streak is light green Its luster is vitreous, its hardness, i 5-2 5
and sp gr =3
Before the blowpipe it melts to a gray globule and gives the arsenic
odor In the closed glass tube it blackens and yields water In the
beads it gives the usual reactions for Ni The mineral dissolves easily
in acids
Synthesis —Crystals have been produced by the method employed
in the synthesis of erythnte, using NiSO-i, instead of CoSC>4
Occurrence — It is found as a common alteration product of nickel-
bearing minerals, in the oxidized portions of veins
Localities — Its best known occurrences are m Allemont, Dauphme,
Annaberg and Schneeberg, Saxony, Cobalt, Ontario, and mines in
Colorado and Nevada.
Variscite (A1P04 2H20)
Vanscite is a bright green mineral that has recently come into use as
a gem material. It is apparently an aluminium phosphate with a
theoretical composition as follows 449 per cent P20r>, 32 3 per cent
AloOa and 228 per cent H^O A specimen of crystallized material from
Lucm, Utah, gave the following analysis
P205 A1203 Fe203 Cr03 V203 H20 Total
44 73 32 40 06 18 32 22 68 100 37
Recent investigations indicate that the compound A1P04 2H20 is
dimorphous Both forms are orthorhombic but one, vanscite, has the
properties described under this heading The other, lucinite, is associ-
ated with vanscite, near Lucm, Utah. It, however, occurs in crystals
that are octahedral in habit, rather than tabular, and that have an
axial ratio of 8729 i 9788 In other respects lucimte is very much
like variscite
An amorphous variety of the same substance is also known It
occurs as a white, pale brown or pale blue earthy mass with a sp gr of
2.135 It differs from the crystalline varieties in being completely
soluble in warm concentrated H2S04
The crystals of vanscite are orthorhombic and are bounded by
co P 66 (oio), oo P(no) and £P oo (012), and in a few cases oo P 60 (too)
Their axial ratio is 8944 .1:1 0919 Nearly all crystals are tabular
parallel to oo P 56 (oio) Twins are common, with |P 60 (102) the
twinning plane Crystals are comparatively rare, the mineral occur-
ring usually in fibrous or finely granular masses and as incrustations
PHOSPHATES, ARSENATES AND VANADATES 285
Vanscite vanes in color from a pale to a bright green It is weakly
pleochroic, has a vitreous luster, a hardness of about 4 and a density of
2 54 Its refractive indices for yellow light are a=i 546, /3=i 556,
r=i 578
Before the blowpipe the mineral is infusible It, however, whitens
and colors the flame deep bluish green It )ields water in the closed
tube, and with the loss of its water, it changes color from green to
lavender The same change in color takes place gradually at temper-
atures between iio°-i6o° When heated with Co(N03)2, it turns blue
and when fused with magnesium ribbon it gives the test for phosphorus
It forms a yellowish green glass with borax or microcosmic salt. The
mineral is insoluble in acids before heating
Vanscite resembles m some respects certain varieties of turquoise
and wwuellite (p 287) It is distinguished from turquoise by the absence
of copper and from wavellite by its insolubility in acids
Occurrence — The mineral occurs as a cement in a brecciated, cherty
limestone and a brecciated rhyolite, as nodules m the cherty portions
of the breccias and also as veins traversing these rocks It is also
found as nests in weathered pegmatites The crystals occur as coarsely
granular, loosely coherent masses in more compact granular masses
Localities — Vanscite occurs at Messbadi, Sa\ony, in Montgomery
County, Arkansas, near Lucm, Utah, and at a number of other places
in Tooele and Washington Counties in this State, in Esmeralda County,
Nevada, and m Montgomery County, Arkansas The colloidal vanety
occurs as concretions in slates at Brandberg, near Leoben, Austria
Uses — The mixture of vanscite and rock is cut, and employed as
sets in necklaces, belt pins, etc , under the names " utahlite " and
" amatrice," but because of the softness of the vanscite it cannot be
used with success for all the purposes for which turquoise matrix is
used
Production — The production of the material in the United States
during 1911 was 540 Ib , valued at $5,750 In the previous year
5,377 Ib were reported as having been sold for $26,125, In I9I2>
the amount marketed was valued at $8,150.
Skorodite
Skorodite is more common than viviamte It occurs in globular
and earthy masses, as incrustations, and in crystals of a green or brown
color The globular forms are colloidal
Its formula indicates Fe203=346 per cent, Asa03=498 Per cent
286 DESCRIPTIVE MINERALOGY
and HoO= 15 6 per cent An incrustation on the deposits of the Joseph's
Coat Spring, Yellowstone National Park, consisted of
As2O5 Fe2O3 H2O SiO2 SO3 Total
46 48 33 29 I5 5° 4 35 84 100 46
Its crystallization is orthorhombic (bipyramidal class), with a b . c
— 8658 . i 9541. The crystals, which are commonly bounded by
oo P 60(100), oo P 06(010), ooPa(i2o), ooP(uo),
P(III) and -2-P(ii2), are either prismatic or octa-
hedral m habit (Fig 159) The angle niAiTi
= 65° 20' Their cleavage is imperfect, parallel to
ooP(no)
The mineral is brittle It has a vitreous luster,
a leek-green or liver-brown color and a white
streak. It is translucent and has an uneven frac-
ture Its hardness is 3 5-4 and density about 3 3
FIG 159 —Skorodite The colloidal phases are somewhat softer than the
Crysta wit oo co , crysta}}me phases
100 (a) oo P 2, 1 20
(d) and P m (p) In "the closed tube skorodite turns yellow and
' yields water It fuses easily, coloring the flame
bluish. On charcoal it yields white arsenical fumes and gives a black
porous, magnetic button It is soluble in HC1, forming a brown solution
It is distinguished from wviamte by the arsenic test, and from dufren-
%te by its streak and reaction in the closed tube
Synthesis — Skorodite crystals have been made by heating metallic
iron with concentrated arsenic acid solution at I4o0~i$o0
Occurrence. — Skorodite is frequently associated with arsenopynte,
in the oxidized portions of veins containing iron minerals It is found
also in a few places as incrustations deposited by hot springs,
Localities — It occurs m fine crystals at Nerchinsk, Siberia; at
Loelling, m Cannthia, near Edenville, New York, in the Tmtic dis-
trict, Utah, and as an incrustation on the siliceous sinter of the geysers
in Yellowstone Park.
HYDRATED BASIC PHOSPHATES AND ARSENATES
The hydrated basic phosphates and arsenates are rather more nu-
merous than the hydrated normal compounds, but most of them are rare
One, waveltite, however, is a handsome mineral that is fairly common.
Another, pharmacosiderite, an iron arsenate, is known to occur at a
number of places The uramte group also belongs here Its members
PHOSPHATES, ARSENATES AND VANADATES 287
are comparatively rare, but, because of the presence of uranium in them,
they are of considerable interest
Wavellite ((A1(OH F)3)(PO4)2 5H2O)
Wavellite rarely occurs in crystals It is usually in acicular aggre-
gates that are either globular or radiating (Fig 160) The few crystals
that have been seen are orthorhombic (bipyramidal class), with an
axial ratio of 5573 i . 4057
Its composition varies widely, and frequently a fairly large portion
of the OH is replaced by F, and a portion of the Al by Fe
The mineral is vitreous in luster and white, green, yellow, brown or
black in color Its streak is white It is brittle and translucent, m-
FIG 1 60 — Radiate Wavellite on a Rock Surface
fusible and insoluble m acids Its hardness is 3 5 and its density 2.41.
Its intermediate refractive index for yellow light is i 526.
Heated m a dosed glass tube, wavelhte yields water, the last traces
of which react acid and often etch the glass In the blowpipe flame the
mineral swells up and breaks into tiny infusible fragments, at the same
time tingeing the flame green. The mineral is soluble in HC1 and
H2SO4. When heated with HaS04 many specimens yield hydrofluoric
acid When heated on charcoal and moistened with Co(NOs)2 and
reheated, the mineral turns blue.
Wavellite is distinguished from turquoise, which it sometimes
resembles, by its action in the blowpipe flame, by its inferior hardness
and its manner of occurrence
Occurrence — Wavellite occurs as radiating bundles on the walls of
288 DESCRIPTIVE MINERALOGY
cracks in various rocks and as globular masses filling ore veins and the
spaces between the fragments of breccias It is probably m all cases
the result of weathering
Localities —It is found at a great number of places, especially at
Zbirow, in Bohemia, at Mmas Geraes, Brazil, at Magnet Cove, Arkan-
sas, and in the slate quarries in York County, Penn.
Pharmacosidente ((FeOH)3(AsO4)2 5H2O)
Pharmacosiderite is a hydrated ferric arsenate, the composition of
which is not firmly established It usually occurs m small isometric
crystals (hextetrahedral class), that are commonly combinations of
ooQoo(ioo) and — (in) It is also sometimes found in granular
i
masses Its cleavage is parallel to oo 0 °o (100)
The mineral is green, dark brown or yellow. Its streak is a pale
shade of the same color It has an adamantine luster and is translucent.
Its hardness = 25 and sp gr =3 It is sectile and pyroelectnc Its
refractive mde\, «=i 676
Pharmacosiderite reacts like skorodite before the blowpipe and with
reagents
The mineral occurs m the oxidized portions of 01 c \ ems, in Cornwall,
England, at Schneeberg, Saxony, near SchemmU, Hungai} , and in the
Tintic district, Utah.
URANITE GROUP
The uramtes are a group of phosphates, arsenates and vanadates
containing uranium m the form of the radical uranyl (UOs) which is
bivalent The members of the group are either tetragonal, or ortho-
rhombic with a tetragonal habit They all contain eight molecules of
water of crystallization Only three members of the group are of
sufficient interest to be discussed here These are the hydrated cop-
per and calcium uranyl phosphates, torbermte and aittumte and the
potassium uranyl vanadate, carnotite
The entire group so far as its members have been identified is as
follows.
Awlumte Ca(U02)2(P04)2 8H20 Orthorhombic
Uranospwite Ca(U02}2(As04)2 SBfcO Orthorhombic
Torb&rmte Cu(U02)2(P04)2 8H20 Tetragonal
Zeunente Cu(U02)2(As04)2 8H20 Tetragonal
Uranocirate Ba(U02)2(P04)2 8H20 Orthorhombic
Camohte (Ca
PHOSPHATES, ARSENATES AND VANADATES 289
The uramtes are of interest because of their content of uranium, an
element which is genetically related to radium
Autunite (CaCUCbMPO^ 8H2O)
Autunite occurs in thin tabular crystals with a distinctly tetragonal
habit, and in foliated and micaceous masses
The percentage composition corresponding to the above formula
is 6 i per cent CaO, 62.7 per cent UOs, 15 5 per cent PsOs and 15 7 per
cent H2O
Its crystals are orthorhombic (bipjrraimdal class), with an axial
ratio, p875 : i 28517, thus possessing interfacial angles that closely
approach those of torbermte. Its crystals are bounded by oP(ooi),
P a (101), P 06 (on), and several less prominent planes Their cleav-
age is very perfect and the cleavage lamellae are brittle The luster is
pearly on the base and vitreous on other surfaces.
The mineral is lemon-yellow or sulphur-yellow in color, and its streak
is yellow It is transparent to translucent. Its hardness is 2-2 5 and
its specific gravity about 3 2. Its refractive indices for yellow light are.
« = i 553,0=1 S7S>7=i577
The mineral reacts like torbermte before the blowpipe and with acids,
except that it shows none of the tests for copper. It is recognized by its
color, streak and specific gravity
Occurrence — Autunite occurs m pegmatite veins and on the walls
of cracks in rocks near igneous intrusions, especially in association with
other uranium compounds, of which it is a decomposition product.
Localities. — It has been found at Johanngeorgenstadt, Germany,
at Middletown and Branchville, Conn , in the mica mines of Mitchell
County, North Carolina, and coating cracks in gneiss at Baltimore, Md
Torbernite (CuCUOs^CPO^ -8H20)
Torbermte occurs in small square tables, that may be very thin or
moderately thick, and in foliated and micaceous masses.
The pure mineral contains 612 per cent UOs, 8 4 per cent Cu,
15 i per cent P20s and 15.3 per cent H2<D, but frequently a part of the P
is replaced by As
Its crystals are tetragonal (ditetragonal bipyramidal class), with
a c= i . 2 9361 They are extremely simple, their predominating
forms being oP(ooi) and POD (101). Less prominent are ooPoo (100),
sPoo(2oi) and ooP(no) Their cleavage is perfect parallel to oP
The cleavage lamellae may be almost as thin as those of the micas
but they are brittle
290 DESCRIPTIVE MINERALOGY
The mineral is bright green in emerald, grass or apple shades, has a
lighter green streak, is translucent or transparent, and has a hardness
of 2 25 and a specific gravity of about 3 5 Its luster is pearly on the
basal plane but nearly vitreous on other burfaces It is strongly pleo-
chroic in green and blue.
Torbermte gives reactions for Cu and P and yields water in the
closed tube The bead reactions for uranium are masked by those of
copper The mineral is soluble in HN03
The mineral is easily recognized by its color and other physical
properties
Occurrence. — Torbermte is occasionally found as a coating on the
walls of crevices in rocks It occurs in Cornwall, England, at Schee-
berg, Saxony, at Joachimsthal, Bohemia, and at most places where other
uranium minerals exist It is probably in all cases a weathering product.
Carnotite ((Ca KsXTTC^MVO^ xHaO)
Carnotite, like the other uramtes described, is extremely complex
in composition It may be an impure potassium uranyl vanadate, or a
mixture of several vanadates in which the potassium uranyl compound
is the most prominent The formula given above indicates its com-
position as well as any simple formula that has been proposed A
specimen from La Sal Creek, Colorado, shows the mineral to be essen-
tially as follows '
UOs CaO BaO K20 H20 at 105° H20 above 105°
18 05 54 oo i 86 i 86 5 4^ 3 16 2 21
though there are present in the specimen analyzed, or in other specimens
from the same locality, also As203, P2O5, Si02, Ti02, C02, S03, Mo03,
Cr203, Fe203, A1203, PbO, CuO, SrO, MgO, Li20 and Na20, and there
are reported in them also small quantities of radium Radiographs
taken with the aid of carnotite have been published, which are almost
as clear as those taken with pitchblende The complete analysis of a
specimen from the Copper Prince Claim, Montrose Co , Colo , gave:
V205
1835
CuO
20
Also
Na20=
As205
25
CaO
285
TiOa=.
.09
P205
33
BaO
.72
10, C02=
U03 MoOg Fe203
52 25 23 i 77
K20 H20- H20+
6 73 2 59 3 06
33, S03=.i2, CrOs=tr,
A1203
i. 08
Ins
8 34
MgO=
PbO
25
Total
99 84
20 and
PHOSPHATES, ARSENATES AND VANADATES 291
The mineral has been found only in tiny crystalline grams, so that its
physical properties are not well known It is bright yellow in color, and
is completely soluble in HNOs If to the nitric acid solution hydro-
gen peroxide be added a brown color will appear Or if the solution
is filtered, made alkaline by ammonia and through it is passed H2S, a
garnet color will develop If the mineral be moistened by a drop of
concentrated HC1, a rich brown color will result The addition of a drop
or two of water will change the color to light green or make it disappear
Occurrence — Carnotite occurs as a yellow crystalline powder, some
of which seems to consist of minute crystals with an hexagonal habit,
in the interstices between the grains in sandstones and conglomer-
ates, as nodules or lumps in these rocks, and as coatings on the walls
of cracks in pebbles in the conglomerates and on pieces of silicified
wood embedded in the sandstones. It is limited to very shallow
depths and is apparently a deposit from ground water.
Localities — Its principal known occurrences are in Montrose, San
Miguel, Mesa and Dolores Counties in southwestern Colorado, especially
in Paradox Valley, and in adjoining portions of New Mexico and Utah,
and in Rio Blanco and Routt Counties in the northwestern portion of
Colorado. At all these places there are large quantities of the impreg-
nated rock but it contains on the average only about i 5 per cent to
2 per cent of UsOg. The mineral has also been described from Mt
Pisgah, Mauch Chunk, Pennsylvania, and from Radium Hill, South
Australia
Uses. — The mineral is one of the main sources of radium and uranium
and is one of the principal sources of vanadium. Although it contains a
notable quantity of uranium, carnotite has little value except as an ore
of radium and vanadium, because of the few uses to which uranium is
put. This metal is used to some extent in making steel alloys and in the
manufacture of iridescent glazes and glass Its compounds are used in
certain chemical determinations, as medicines, in photography, as por-
celain paint, and as a dye in calico printing. The uses of vanadium have
been referred to on p 273
The principal value of carnotite depends upon its content of radium,
which in the form of the chloride is valued at about $40,000 per gram
or $1,500,000 per oz The importance of radium as a therapeutic agent
has not been established, but that its use is wonderfully helpful in many
diseases is beyond question Without doubt in the near future carno-
tite will become the principal source of radium in the world Practically
the only other source is the pitchblende (p 297), of Gilpin, Colorado,
Cornwall, England and Joachimsthal, Austria.
292 DESCRIPTIVE MINERALOGY
Production — Carnotite has been mined in San Miguel and Montrose
Counties, Colorado, and at several points in eastern Utah, but mainly
for the vanadium it contains At present it is being utilized as a source
of radium From Colorado 8,400 tons of vanadium ore, with a value
of $302,000, were shipped in 1911 and from New Mexico and Utah about
70 tons, valued at $3,500 Some of this, however, was vanadmite
Most of it was exported and used as a source of vanadium However,
the uranium content of the carnotite mined was about i r tons of the
metal During 1912 ore containing 26 tons of uranium o\ide and 6 7
grams of radium was produced This would have yielded n 43 grams
of radium bromide, valued at $52,800 The present price of standard
carnotite carrying at least 2 per cent UgOg and 5 per cent V^Os, is at the
rate of $i 25 per Ib for the former and thirty cents for the latter In
1914 the selling price of 4,294 tons of carnotite ore containing 87 tons
of UsOg was $103 per ton At the present time nothing is paid for the
radium content of the ore, though this is its most valuable component
One ton of ore containing i per cent of UaOg carries 2 566 milligrams of
radium The imports of uranium compounds during 191*2 were valued
at $14,357-
HYDRATED ACID PHOSPHATES AND ARSENATES
A number of hydrated acid phosphates and arsenates are known to
constitute an isomorphous group, but only a few of them occur as
minerals. Brushite is an acid calcium phosphate and pfwrmacofate is
the corresponding arsenate Both crystallize in the monoclimc system
(prismatic class) Neither is common
Pharmacohte (HCaAs04 2H20) occurs principally in silky fibers, in *
botryoidal and stalactic masses and rarely in crystals with an axial
ratio .6236 ' i : 3548 and 18=83° 13'. Their cleavage is perfect par-
allel to oo P ob (oio) The mineral is white or gray, tinged with red
Its streak is white It is translucent or opaque Its luster is vitreous,
except on oo P & (oio) where it is slightly pearly Thin laminae are
flexible Its hardness is 2-2 5 and density 2 7 Its refractive indices
for yellow light are. 01=1.5825, ]8=i 5891, 7=1 5937
Before the blowpipe pharmacohte swells up and melts to a white
enamel. The mineral gives the usual reactions for As, EfeO and Ca It
usually occurs in the weathered zone of arsenical ores of Fe, Ag and Co,
at Andreasberg, Harz; Joachimsthal, Bohemia, and elsewhere.
CHAPTER XV
THE COLUMBATES, TANTALATES \ND URANATES
THE rare metah, columbium and tantalum, exist in a few silicates,
but their principal occurrences are as columbates and tantalates which
are salts of columbium and tantalum acids, analogous to the various
acids of sulphur The commonest compounds are salts of the meta-
acids EfeQteOo and H2Ta20e, the relations of which, to the normal acids,
are indicated by the equation 2HsCb04— 2H20=H2Cb206 Other im-
portant minerals are derivatives of the pyroacids corresponding to
HiCtaOr, or 2HsCb04— EkO The best known ortho salt is ferguson-
tte, YCb04, but it is rare
All the columbates yield a blue solution when partially decomposed
in EfeSQi and boiled with HC1 and metallic tin The tantalates when
fused with KHSO* and treated with dilute HC1 give a yellow solution
and a heavy white precipitate, which, on treatment with metallic zinc
or tin, assumes a deep blue color When diluted with water the blue
color of the tantalate solution disappears, whole that of the columbate
solution remains
The uranates are salts of uramc acid, HsUtX. The only mineral
known that may be a uranate is urarnn/Ue9 and the composition of this
is doubtful.
Columbite (CFe-Mn)Nb2O6) and Tantalite ((Fe-Mn)Ta2O6)
These two minerals are isomorphous mixtures of iron and manganese
columbates and tantalates The name columbite is applied to the mix-
ture that is composed mainly of the columbates, and tantalite to that
which is principally a mixture of tantalates When the tantalite is
composed almost exclusively of the manganese molecule, it is known as
manganotantal^te Tin and tungsten are frequently found in both min-
erals
Their crystals are orthorhombic, with a : b . c— 8285 : i : 8898 for
the nearly pure columbium compound, and 8304 : i : .8732 for the
nearly pure tantalum compound Both form short prismatic crystals
containing many faces, among the most prominent being the three
pinacoids, various prisms, notably °o P(no), oo Pjfoo) and oo P6(i6o),
294
DESCRIPTIVE MINERALOGY
and the domes 2? 56 (201) and |P 06 (012) (Fig 161) The most promi-
nent pyramids are P(in) and P3(i33). Twins are not uncommon,
with 2P66 (201) the twinning plane The angle noAiIo for colum-
bite=79° 17'
Both minerals are usually opaque, black and lustrous, and occasion-
ally iridescent, though, in some instances, they are translucent and
broun Their streak is dark red or black Their cleavage is distinct
parallel to oo P 60 (100), fracture uneven or conchoidal, their hardness
6 and their specific gravity
between 5 3 and 73, in-
creasing with the propor-
tion of the tantalum mole-
cules present They are
both infusible before the
blowpipe Some specimens
exhibit weak radioactivity
When columbite is de-
composed by fusion with
KOH and dissolved in HC1
and BkSO-i, the solution
turns blue Qn thfi addltlon
USbdllC «1C The mm-
eral 1S also partially decom-
posed when evaporated to
dryness with EfeSCU, forming a white compound that changes to yellow
When this residue is boiled with HC1 and metallic zinc a blue solution
results The mineral also gives reactions for iron and manganese.
Tantalite is decomposed upon fusion with KHSQ* in a platinum
spoon, or on foil. This when heated with dilute HCl yields a yellow
solution and a heavy white powder Upon addition of metallic zinc, a
blue color results and this disappears on dilution with water In the
microcosmic salt bead tantalite dissolves slowly, giving reactions for iron
and manganese When treated with tin on charcoal the bead turns
green
The two minerals may easily be confused with black fourmahne
(p. 434), tlmemte (p 462) and wolframite From tourmaline, they are
distinguished by crystallization, high specific gravity and luster, from
wolframite by their less perfect deavage and by the reaction with
aqua regia (see p 259), from ilmenite by the test for titanium
Occurrence, Ongm and Localities.— Both minerals occur in veins of
coarse granite and probably have a pneumatolytic origin
FIG i6i.-Columbite Crystals with
(a). ooPoo,oio (6), oop, no (f»), °oP2, 210
Ml -« 730 (d), oop^o (,), |P 55, I03
(«, P, in W and PI 133 M
COLUMBATES, TANTALATES AND URANATES 295
Columbite is found in granite \erns at Bodenmais, Bavaria, Tam-
mela, in Finland, near Limoges, France, with tantahte, near Miask,
in the Ilmen Mountains, Russia, with samarskite, and at Ivigtut, m
Greenland In the United States it is found at Standish and Stone-
ham, m Maine, at Acworth, in New Hampshire, at Haddam, in Con-
necticut, at Amelia Court House, Virginia, with samarskite in the mica
mines in Mitchell County, North Carolina, m the Black Hills, South
Dakota, and at a number of other points in New England and the Far
West
Tantahte is found at many of the localities for columbite and also
at several other places in Finland, near Falun, in Sweden, in Yancy
County, North Carolina, and m Coosa County, Alabama
Uses — At the present time columbium and its compounds have no
commercial uses Tantalum, however, is employed in the manufacture
of filaments for certain types of incandescent lamps Since, howe\er,
about 20,000 filaments may be made from a single pound of the metal the
market for tantalum ores is very limited
Samarskite and Yttrotantalite
These two minerals may be regarded as isomorphous mixtures of
salts of pyrocolumbic and pyrotantalic acids, in which the bases are
yttrium, iron, calcium and uranyl.
Samarskite, according to this view, is approximately
Y2(Ca Fe U02)3(Nb207)3
and yttrotantalite the corresponding tantalate Yttrium and iron are
the principal bases, but there are also often present erbium, cerium,
tungsten and tin
Analyses made by Rammelsberg and quoted by Dana give some idea
of the complexity of the compounds:
Density
Ta206 Nb205 W03
Sn02 Ti02* Y203
Er20a
I 5 425
46 25
12 32 2 36
I 12
10.52
6 71
II- 5 839
14 36
41 07
16
56 6 10
10 80
III 5 672
•
55 34
22
i 08 8 80
382
Ce203t
U02
FeO
CaO
H2O
Total
I 2 22
i 61
380
5 73
6 31
98 95
II. 2 37
10 90
14 61
.
too 93
HI 4 33
ii 94
14 3°
•
99 83
I Fromltterb;
y, Sweden
II From North Carolina
HI From Miask
Russia.
* Including SiO*, f Including Di20s and La^Os
296 DESCRIPTIVE MINERALOGY
The first of these three minerals has been called yttrotantahte and
the other two samarslute If the first is weathered, as seems probable
from the presence of over SL\ per cent of water, the three may constitute
members of an isomorphous series with the third representing the nearly
pure columbate (sanurskite), the first a compound in which the tantalate
molecule is in excess (yttrotantahte), and the second an intermediate
compound which contains both the tantalum and columbmm molecules,
with the latter predominating
With more accurate analyses the great complexity of these compounds
becomes even more apparent Hillebrand has given the following report
of his analysis of a samarskite from Devil's Head Mountain, near Pike's
Peak, Colorado, which shows the futility of attempting to represent its
composition by a chemical formula-
Pitch-black Black Weathered
Variety Variety Variety
Ta20fi 27 03 28 ii 19 34
CbaOs 27 77 26 16 27 56
W03 2 25 2 08 5 51
SnO2 95 i 09 82
Zr02 2 29 2 60 3 10*
U02 4 02 4 22
U03 6 20
Th02 3 64 3 60 3 19
Ce203 54 49 4i
(La,Di)203 I 80 2 12 i 44
Er20s 10 71 10 70 9 82
Y203 6 41 5 96 5 64
Fe203 8 77 8 72 8 90
FeO 32 35 39f
MnO 78 75 \
ZnO 05 07 / 77
PbO 72 80 i 07
CaO 27 33 i 6 1
MgO „
K20 17 I3 •>
(Na,Li)20 24 17 I ^
H20.. i 58 i 30 3 94
F . ? ? ?
99 75
6 12
f O
COLUMBATES, TANTALATES AND URANATES 297
Poo,ioi(e),
3P3> 231 W
120
Both samarskite and yttrotantahte are orthorhombic, with an axial
ratio for samarskite of 5456 : i : 5178, and for yttrotantahte, 5411 •
i . i 1330. They, however, more commonly occur massive and in
flattened grams embedded in rocks Their crystals are prismatic in
the direction of the c or the b a\is Their most prominent forms are
oo P 56 (100), oo P 66 (oio) and P 65 (101) (Fig 162) Less prominent
but fairly common are *>P2(i2o), ooP(no), P(in) and
The angle noAiTo for samarskite is 57° 14'
and for yttrotantahte 56° 50'
The cleavage of both minerals is indistinct
parallel to oo P 06 (oio) Their fracture is
conchoidal Both are brittle The hardness of
samarskite is 5-6, its density about 5 7, its
luster vitreous, its color velvety black and its
streak reddish brown Yttrotantahte is a little
softer (5-5 5) Its specific gravity is 5 5~5 9,
its luster submetallic to vitreous, its color black, FIG 162 — SamarshteCiys-
brown, or yellow, and its streak gray to color- fed w^ oop 55 , 100 (a),
less Samarskite is opaque and yttrotantahte °°p55' OI° JW> °°p»
opaque or translucent
The reactions of the minerals vary with
their composition They always yield the
blue solution test for tantalum or columbium, and most specimens react
for Mn, Fe, Ti and U The reaction for uranium is an emerald green
bead with microcosmic salt in both reducing and oxidizing flame.
They are distinguished from columbite and t&ntahte by the form of
their crystals.
Occurrence — The two minerals, like columbite and tantahte, are
found principally in pegmatite veins and in many of the same localities
Yttrotantahte occurs mainly at Ytterby and near Falun, in Sweden, and
samarskite, near Miask in the Ilmen Mountains, Russia, In the United
States the last-named mineral is sometimes found in large masses in the
mica pegmatites of Mitchell County, North Carolina.
Uses — Neither mineral is at present of any commercial value. They
are, however, extremely interesting as the source of many of the rare
elements, and, especially, as a possible source of radium and closely
related substances.
Urardnite
Uramnite, or pitchblende, like the other compounds containing the
element uranium, is of doubtful composition. It contains so many
298 DESCRIPTIVE MINERALOGY
different components that a correct conception of its character is almost
impossible to grasp The mineral is particularly interesting because it
always contains a trace of radium, of which it is an important com-
mercial source at the present time
Analyses of crystallized material (I) from Branchville, Conn,
and from Annerod (II), Norway gave the following results
U03 U02 ThO2 PbO Fe2O3 CaO H2O Pie Insol
I. 21 54 64 72 6 93 4 34 28 22 67 Und. 14
II 30 63 46 13 6 oo 9 04 25 37 74 17 4 42
\\ith small quantities also of ZrC>2, Ce02, La203, D^Os, YgOs, Er2C>3,
MnO, Alkalies, SiOs and P20s These analyses are interpieted as indi-
cating that the mineral is a uranium salt of uramc acid, U02(OH)2, or
H2U04, thus U^dr , or U30S, in which Pb replaces the U in
part, and Th02 the UC>2 Radium is found in most specimens and
helium in nearly all
Several varieties aie recognized, the distinctions being based largely
upon chemical differences
Broggente has UOa to other bases as i : i
Cleweite and nnvemte contain 9 per cent to 10 per cent of the yttna
earths
Pitchblende is possibly an amorphous urammte containing a very
little thona and much water Its specific gravity is often as low as 6 5,
due probably to partial alteration
Urammte crystallizes in the isometric system in octahedrons, and m
combinations of 0(ui), oo 0(no), and oo 0 oo (100) Crystals are rare,
however, the material usually occurring in crystalline masses and in
botyroidal groups
The mineral is gray, brown or black and opaque. Its streak is
brownish black, gray or olive green. Its luster is pitch-like or dull Its
fracture is uneven or conchoidal It is brittle, its hardness is 5 5 and
density 9-9 7 Like the other uranium minerals it is radioactive
Before the blowpipe uraninite is infusible. Some specimens color
the flame green with copper With borax it gives a yellow bead in the
oxidizing flame, turning green in the reducing flame All specimens give
reactions for lead and many for sulphur and arsenic The mineral is
soluble in nitric and sulphuric acids, with slight evolutions of helium,
OOLUMBATES, TANTALATES AND URANATES 299
the ease of solubility increasing with the increase in the proportion of
rare earths present
Urammte is distinguished from wo'Jramite, samarsktfe, columbde and
tantahte, by lack of cleavage, greater specific gravity, and differences in
crystallization From all but samarskite it is also distinguished by the
reactions for uranium and, m the case of most specimens, by the reac-
tion for lead It is especially characterized by its pitch-black luster
Occurrence and Localities — Urammte occurs in pegmatites and in
veins associated ^ith silver, lead, copper and other ores It is found m
the ore veins in Saxony, Bohemia, and in pegmatites near Moss, Arendal
and other points in Norway
In the United States it occurs in pegmatites at Middletown and
B ranch ville, in Connecticut, at the Mitchell County mica mines,
North Carolina, and at Barnnger Hill, Llano County, Texas It is
also found m large quantity near Central City, Gilpin County, Colorado,
where it is associated with gold, galena, tetrahednte, chaicopynte and
other ore mineials
Production — Urammte has been mined in small quantity in Colo-
rado, and at Barnnger Hill, both as a source of uranium and as a
source of radium In Cornwall, England, and at Joachimsthal,
Austria, it is mined as a source of radium (See also p 292.)
CHAPTER XVI
THE SILICATES
THE silicates are salts of various silicon acids, only a few of which
are known uncombmed with bases The silicates include the commonest
minerals and those that occur in largest quantity They make up the
greater portion of the earth's crust, forming most of the igneous rocks
and a large portion of vein fillings In number, the silicates exceed all
other mineral compounds, but because of their stability they are of very
little economic importance A few are used as the sources of valuable
substances, and their aggregates, the sihcious rocks, are utilized as
building stones, but, on the whole, they are of little commercial value
Since, however, they occur in good crystals and their material is trans-
parent in thin sections so that it can easily be studied by optical methods,
they are of great scientific importance Much of the progress made in
crystallography has been accomplished through the study of these com-
pounds
Although the salts of the silicic acids are very numerous and most of
them are very stable toward the ordinary reagents of the laboratory,
the acids from \\hich they are derived are only imperfectly known
The only one that has been prepared m the pure state is the compound
KfeSiOa This occurs as a gelatinous (colloidal) white substance which
rapidly loses water upon drying and probably breaks up into a number
of other compounds which are also acids, containing, however, a larger
proportion of silicon in the molecule than that in the original compound
When the tetrafluoride, or the tetrachionde, of silicon is decomposed by
water, the principal product is the acid referred to above, but m addition
to this there is probably formed also the compound HaSiO* or Si(OH)4,
which is the ortho acid Some silicates are salts of these acids. Others
are salts of the acids containing a larger proportion of silicon In most
cases, however, these acids may be regarded as belonging to a series in
which the members are related to one another m the same manner as
are normal sulphuric, common sulphuric and pyrosulphuric acids. Nor-
mal sxilphuric acid is HeSOe By abstraction of aKkO the compound
H2SO4, or ordinary sulphuric acid, results If from two molecules of
EfcSOi, one molecule of HsO is abstracted, 1128307, or pyrosulphuric
acid, is left. In the same manner all of the silicic acids may be regarded
300
SILICATES 301
as being derived from normal silicic acid Si(OH)4 or H4SiO4 by the ab-
straction of water, thus:
Orthosilicic acid is
Metasihcic acid is H4Si04 -I^Oor H2SiOs,
Diorthosilicic acid is 2H4Si04— IfeO or
Dimetasilicic acid is 21*28103- EfeO or
Tnmetasilicic acid is 31128103 — EfeO or
The compounds containing more than one silicon atom in the molecule
are known as polysilicates The salts of metasilicic acid are meta-
sihcates
Many attempts have been made to discover the chemical structure
of the comparatively simple silicates and several proposals have been
offered to explain the great differences often observed in the properties
of silicates with the same empirical formula, but no explanation of these
differences has thus far proved satisfactory The silicates are so very
stable under laboratory conditions, and, when they are decomposed,
their decomposition products are so difficult to study, that it has been
impossible to determine their molecular volumes or to understand their
substitution products We are thus driven to ascribe many of the
anomalies in their composition to solid solutions, to absorption phenom-
ena, and to the isomorphous mixing of compounds, some of which do
not exist independently
There are many silicates, moreover, which cannot be assigned to any
of the simple acids mentioned above, but which probably must be
regarded as salts of very much more complex acids Others are pos-
sible salts of alurninosiliac acids in which aluminium functions in the
acid portions Thus, albite is usually regarded as a trisilicate, NaAlSisOg,
and anorthite as an orthosihcate, CaAl2(Si04)2 But the two substances
are completely isomorphous, and for this reason it is thought that they
must be salts of the same acid If we assume an aluminosilicic acid of
the formula HsAlS^Og, albite may be written (NaSi) AlSi2Og, and anor-
thite (CaAl)AlSi20g The two minerals thus become salts of the same
acid and their complete isomorphism is explained The relations that
exist among many silicates might be better understood on the assump-
tion that they are salts of complex silicic and of aluminosilicic acids
than on the assumption that they are salts of simpler acids, as is now the
case But, since it has been impossible to isolate the acids and study
them we are not certain as to their character It is, therefore, believed
best to represent most silicates as salts of the simplest acids possible,
consistent with their empirical compositions as determined by analyses
302 DESCRIPTIVE MINERALOGY
As in,the case of salts of other acids there are silicates that contain
hydrogen and oxygen m such relations to their other components that
when heated they yield water In some cases this water is driven off at
a comparatively low temperature and the residue of the compound re-
mams unchanged A compound of this kind is usually called a hydrate
or the compound is said to contain water of crystallization In other
cases a high temperature is necessary to drive off water, and the com-
pound breaks up into simpler ones In these instances the water is
said to be combined The compound is usually basic
In the descriptions of the silicates the order in which the minerals are
discussed is that of increasing acidity, i e , increasing proportion of the
Si02 group present m the molecule This order, however, is not fol-
lowed ngorously The members of well defined groups of closely related
minerals are discussed together even if their acidity varies widely
Nearly all the silicates are transparent or translucent and all are elec-
trical insulators
THE ANHYDROUS ORTHOSILICATES
NORMAL ORTHOSILICATES— R4SiO4
OLIVINE GROUP (R"aSi04) R"=Mg, Fe, Mn, Zn
The members of the olivine group are normal silicates of the metals
Mg, Fe, Mn and Zn They constitute an isomorphous series crystalliz-
ing in the holohedral division of the orthorhombic system (rhombic bi-
pyramidal class) The most common member is the magnesium-iron
compound (Mg Fe)2Si04, ohmne, or thrysot Ic, from which the group
gets its name. The members with the simplest composition are for-
st&rite (Mg2Si04), fayahte (FeaSiO^ and tephrotte (Mn2SiOj.) The
others are isomorphous mixtures of these, with the exception of three
rare minerals, of which one, monttcelhte, is a calcium magnesium silicate,
another, tttanohwne, contains Ti in place of a part of the Si, and the
other, roeppente, contains some Zn2Si04 Most of them are formed
by crystallization from molten magmas
Crystals of all the members of the group are prismatic and all have
nearly the same habit They are often flattened parallel to one of the
pinacoids, oo P 56 (oio) or oo P 55 (100) The axial ratios of the com-
moner members are as follows
Forstente a : b . c= 4666 : i : 5868 The angle iioAiTo=$o° 2'
Ohvine = 4658 i : 5865 The angle no A 110=49° 57'
Tephroite = 4600 . i : 5939 The angle no A 110=49° 24'
Fayahte = 4584 : i : 5793 The angle iioAiTo=49°
°
ANHYDROUS ORTHOSILICATES
303
Crystals of olivine are usually combinations of some or all of the following
forms- oo P 56 (100), oo P 06 (oio),
oP(ooi), ooP(no), ooP2(i2o),
Po6 (Oil), 2Po6(o2l), Poo(lOl),
P(ni) and 2P2(i2i) (Fig. 163)
The crystals of fayahte are usually
more tabular than those of olivine,
but forsterite and tephroite crystals
have nearly the same forms The
cleavage of all is distinct parallel
to oo P 66 (oio), less distinct parallel
to oo P oo (100) in olivine, and par-
allel to oP(ooi) in fayahte
The compositions of the pure Mg,
Mn, and Fe molecules are
FIG
163— Olivine Crystals with
ooP, no (m)t oop So, oio (b),
OP, 001 (c), 2P5,02l(&), 00 PI,
120 ($),P oo , ioi (d) and P, in (e)
MgO
MnO
FeO
SiO2
Mg2Si04 Mn2Si04
57 i
70 25
42 9
29 75
Fe2Si04
70 6
29 4
All natural crystals, however, contain some of all the metals indicated
and, in addition, many specimens contain also a determmable quantity
of CaO and traces of other elements
Forsterite, Olivine and Fayalite (MfeSiO* - (Mg Fe)2Si04 -Fe2Si04)
The composition of olivine naturally depends upon the proportion
of the forsterite and fayahte molecules present in it When the propor-
tion of FeO exceeds 24 per cent, the variety is known as hya^derite
A few typical analyses are quoted below
MgO
FeO
CaO
I 51 64
S °i
r 08
II 50 27
8S4
III 48 12
ii 18
12
IV 39 68
22 54
A1203 Si02
42 42 30
41 19
40 39
37 17
Total Sp Gr
100 45 3 261
IOO OO
99 81 3.294
99 39
I From masses enclosed m Vesuvian lava
II Concretion in basalt near Sasbach, Kaiserstuhl
III Grams from glacial debris, Jan Mayen, Greenland
IV Grams from coarse-grained rock, near Montreal, Canada
304 DESCRIPTIVE MINERALOGY
In addition, there are often also present small quantities of Ni, Mn,
and Ti
Forsterite, olivme and fayalite are usually yellow or green in color
and have a vitreous luster. Forsterite is sometimes white and ohvine
often brown. All three minerals become brown or black on exposure
to the air All are transparent or translucent Their streak is colorless
or yellow The fracture of ohvine is conchoidal In the other two
minerals it is uneven Their hardness, density and refractive indices
for yellow light are as follows
Hardness Sp Gr a. ft 7
Forsterite 6-7 3 21-3 33 i 6319 i 6519 i 6698
Olivme. 6 5-7 3 27-3 37 i 6674 i 6862 i 7053
Fayalite 65 4 00-4 14 i 8236 i 8642 i 8736
Before the blowpipe most olivines and forsterites whiten but are in-
fusible Their fusion temperatures are between 1300° and 1450°,
decreasing with increase in iron Fayahte and varieties of ohvine rich
in iron fuse to a black magnetic globule All three minerals are decom-
posed by hydrochloric and sulphuric acids with the separation of gelat-
inous silica , the iron-rich vaneties are decomposed more easily than
those poor m iron
The minerals are characterized by their color and solubility m
acids.
Both fayalite and ohvine alter on exposure to the air, the former
changing to an opaque mixture of Fe20s and Si02, or to the fibrous
mineral anthophylhte ((Mg-Fe)SiOs), and ohvine to a mixture of
iron oxides and fibrous or scaly gray or green serpentine (BUMgaS^Oo).
In other cases, under metamorphic conditions, the alteration is to a
red lamellar mineral (iddingsite) which may be a form of serpentine,
or to magnesite, or to the silicate, talc Other kinds of alteration of
this mineral have also been noted but those descnbed are the most
common
Syntheses — The members of the ohvine series have been produced
by fusing together the proper constituents in the presence of magnesium
and other chlorides They are, moreover, present in many furnace
slags where they have been made in the process of ore smelting.
Occurrence — Ohvine occurs as an original constituent of basic igneous
rocks and as a metamorphic product m dolomitic limestones It is
found also in the form of rounded grains in some meteoric irons. Fayalite
occurs in acid igneous rocks, especially where affected by pneumatolytic
ANHYDROUS ORTHOSILICATES 305
action, and forsterite in dolomitic rocks \\hen they have been meta-
morphosed by the action of igneous rocks
Local^t^es — Members of the olivine group occur m the basaltic lavas
of many volcanoes — as those of the Sandwich Islands, in the limestone
inclusions in the lava of Mt Somma, near Naples; in vanous basic
rocks in Vermont and New Hampshire and at Webster, N C. At the
latter place granular aggregates of almost pure ohvme constitute great
rock masses known as dunite
Fayalite is found in the rhyohtes of Mexico, the Yellowstone Park
and elsewhere, and in coarse granite at Rockport, Mass , and in the
Mourne Mountains, Ireland
Forstente occurs in limestone enclosures in the lava of Mt Somma
and at limestone contacts with igneous rocks at Bolton, Roxbury, and
Littleton, Mass , and elsewhere.
Uses and Production.— The only member of the group that is of any
economic importance is a pale yellowish green transparent ohvine, which
is used as jewelry under the name of " peridot " Gem material is found
at Fort Defiance and Rice, in Arizona, scattered loose in the soil The
little grams came from a basic volcanic rock. The amount produced in
the United States during 1912 was valued at about $8,100.
Tephroite (Mn2Si04)
Although tephroite is regarded as the manganese silicate it nearly
always contains some of the forsterite molecule
Analyses of brown (I), and red (II), varieties from Sterling Hill
gave
MnO FeO MgO CaO ZnO Loss SiOs Total
I 52 3* i 52 7 73 * fc> 5 93 28 30 55 99 93
II 47 62 23 14 03 S4 4 77 35 3* 73 99 2 7
The mineral is gray, brown or rose-colored and transparent or
translucent Its streak is nearly colorless It is rarely found m crys-
tals Its hardness is about 6 and its density 408 It is strongly
pleochroic in reddish, brownish red and greenish blue tints Its inter-
mediate refractive index for yellow light = about i 80.
It is fusible with difficulty (fusing temperature =1200°), and is sol-
uble in HC1 with separation of gelatinous silica It is distinguishable
from other like-appearing minerals by its difficult fusibility and its
reaction with HC1
Syntheses — Crystals of the mineral have been made by fusing to-
gether Si02 and Mn02 in the proportion of i : 2, and by long-continued
306 DESCRIPTIVE MINERALOGY
heating of MnCb and Si02 in an atmosphere of moist hydrogen or carbon
dioxide
Localities — -Tephroite occurs at Mine Hill and Sterling Hill, near
Franklin, N J , where it is associated with franldmite, zmcite and
troostite It is found also at Pajsberg in Sweden with other man-
ganese minerals and magnetite, and at Langban, in Wermland,
Sweden
Uses — The mineral is of little commercial value It is separated
with other manganese minerals from the zinc ore of Franklin, N. J , and
is smelted with these in the production of spiegeleisen,
WILLEMITE GROUP CVSiQO R"=Zn, Mn
The willemite group comprises the two minerals willemite (Z^SiO*)
and troostite ((Zn Mn)2SiC>4), of which the latter is rare Willemite
occurs in small quantity only, but troostite is an important source of
zinc at the Franklin locality in New Jersey Both minerals are found in
crystals
Willemite and troostite crystallize m the rhombohedral hemihedral
division of the hexagonal system (ditrigonal scalenohedral class), with
the axial ratios
Willemite a ; c= i : o 6698
Troostite = i . 0.6698
Willemite and Troostite (Zn2SiO4-(Zn Mn)2SiO4)
Willemite and troostite occur massive, in grains, and m simple crys-
tals
The theoretical composition of willemite is 8102—2704 and ZnO
= 72 96, but nearly all natural crystals contain traces of other elements
When a noticeable quantity of manganese is present, the compound
is troostite Several analyses are quoted below
Si02 ZnO MnO FeO Total
Willemite from Stolberg, Germany 26 90 72 91 35 100 16
Willemite from Greenland 27 86 71 51 . 37 99 74
White troostite from Franklin, N J 27 20 65 82 6 97 23 100 22
Dark red troostite from Franklin, N J 27 14 64 38 6 30 i 24 99,00"
The crystals of willemite exhibit the forms ooR(ioTo), oop2(ii2o),
oR(oooi),|R(3034) and -|R(oil2)(Fig 164). Twins, with$P2(3 3 6 10)
as the twinning planes, are rare The crystals of troostite are even
more simple, with oop2(ii2o) and R(ioli), usually the only forms
ANHYDROUS ORTHOSILICATES 307
present, though -JR(oiT2), -^(0332) and R3(2i3i) are also occa-
sionally found The angle ion A 1101 = 63° 59' The cleavage of
willemite is distinct parallel to oP(oooi), and of troostite distinct
parallel to ooP2(ii2o), and less perfect parallel to R(ioTi) and
cR(oooi)
Willemite is colorless, yellow, brown or blue Troostite is green,
yellow, brown or gray The colored varieties of both minerals are
translucent Colorless willemite is transparent Both minerals are
vitreous in luster Their hardness is between
5 and 6 and density between 3 9 and 4 3 The
refractive indices of willemite for yellow light
are w=i 6931, e=i 7118
Both minerals glow when heated before the
blowpipe and are fused with difficulty (about
1484°), and both gelatinize with HC1 Willem-
ite gives the reaction for zinc with Co(NOa)2
on charcoal, and troostite gives, in addition,
the reaction for manganese. FIG 164— Willemite Ciys-
Syntkeses— Willemite crystals have been' td with -Pa, XMO (c),
made by the action of gaseous hydrofluo- W and ~
silicic acid upon zinc, and by the action of
silicon fluoride on zmc oxide at cherry-red temperature
Localities and Origin — Willemite occurs in comparatively small quan-
tity at only a few places, associated with other zinc minerals. In
America it is found in colorless and black crystals at the Merritt
Mine near Socorro, New Mexico, associated with mimetite, wulfenite,
cerussite, bante and quartz
Troostite occurs only at Sterling Hill and Franklin Furnace, N J ,
but in such large quantity that it constitutes an important proportion
of the zmc ore for which these localities are noted It is associated with
franklmite and zincite. Both willemite and troostite are results of
magmatic processes.
Phenacite (Be2Si(>4)
The theoretical composition of the compound B^SiO* is SiO4= 54 47,
BeO=45 S3 Many of the analyses of phenacite show that it ap-
proaches very closely to this. A specimen from Durango, Mexico, for
example, is:
SiO= 54 71, BeO=45 32, MgO+CaO= 14- Total- 100 17.
308 DESCRIPTIVE MINERALOGY
Phenacite crystallizes in the rhombohedral tetartohedral division of
the hexagonal system with a : c= i i 0661 It occuis m crystals pos-
sessing many different types of habit and with many different combina-
tions of forms Perhaps oop2(ii2o), ooP(ioTo), R(ioTi), R3(2i3i)
and — |R(oil2) are the most common (Fig 165) Interpenetration
twins are common at some localities The
cleavage is indistinct parallel to oo P(ioTo)
The angle loTi A^IOI = 63° 24'
Phenacite is colorless or white or some
light shade of yellow or pink. It is trans-
parent or translucent and has a glassy luster
Its hardness is 7 5, and density about 3 and
the refractive indices for yellow light are
FIG ^-Phenacnte Crystal «-' «54*, -i 6700 It'a infusible and
with oo p2, 1 1 20 (a), OOP, insoluble in acids When heated with a
-IPs - - little soda before the blowpipe it affords a
ioTo (m) and -j-r, 1322 ^^ ^^^ ^ ^^j ^ phosphores_
cent and pyroelectric
Colorless phenacite resembles quartz and Jerdente, and the yellow
vanety topaz It is best distinguished from them by its crystalliza-
tion
Syntheses — Small crystals have been made by the fusion of a mix-
ture of Si02 and beryllium oxide and borax, and by melting together
beryllium nitrate, silica and ammonium nitrate
Localities. — Phenacite occurs at the Emerald Mines near Ekaterin-
burg in the Urals, near Fremont, in the Vogesen, at Reckmgen, in
Switzerland, in Durango, Mexico, near Pike's Peak, at Topaz Butte,
and at Mount Aratero, in Colorado, and at Greenwood, m Maine. In
all cases the mineral is probably a result of pneumatolysis
Uses. — The colorless phenacite is used to a slight extent as a gem
GARNET GROUP
(R"3R"'2(Si04)8) R"=Ca, Mg, Fe, Mn R'"=Al, Fe, Cr
The garnet group comprises a large number of isomorphous com-
pounds, some of which are very common The members nearly all
occur in distinct crystals that are combinations of isometric holohedrons
(hexoctahedral class) Many different names have been given to the
garnets and analyses show that they possess very different compositions
With the exception of a few rare varieties, they can all, however, be
explained as consisting of one of the six molecules indicated below, or of
ANHYDROUS ORTHOSILICATES 309
mixtures of them The six molecules and the names of the garnets
corresponding to them, together with their densities, are.
Caa Ala (8104)3 Grossulante or Hessomte Sp gr =3 4-3 6
Mg3Al2(Si04)3 Pyrope =37-38
MnaAk (8104)3 Spessattite ==41-43
Almandite =4 1-4.3
4)3 Andradite or Melamte =3 8-4 i
3 Uvarovite =34
The following table contains the calculated percentage composition
of the several pure garnet molecules and the records of analyses of some
typical varieties of the mineral
SiOs A12O3 FcfcOs Cr203 FeO MgO CaO MnO TiCfe Total
Ia 40 01 22 69 37 30 100 oo
Ib 42 01 17 76 5 06 13 35 01 20 100 17
IIa 44 78 25 40 29 82 100 oo
lib 40 92 22 45 5 46 8 ii 17 85 5 04 46 100 39
Ilia 36 30 20 75 . 42 95 100 oo
Illb 36 34 12 63 4 57 47 I 49 44 20 99 70
IVa 36 15 20 51 43 34 100 oo
IVb 37 61 22 70 33 83 3 61 i 44 i 12 100 31
Va 35 45 3i 49 33 06 100 oo
Vb 35 09 tr 29 15 2 49 24 32 80 36 100 48
Vc 26 36 22 oo i 25 30 72 tr, 21 56 101 89
Via 38 23 29 27 29 27 100 oo
VIb 36 93 5 68 i 96 21 84 i 54 31 63 99 58
Ia Theoretical composition of the grossulante molecule
Ib Green and red grossulante from the limestone at Santa Clara, Cal.
IIa Theoretical composition of the pure pyrope molecule
lib Pyrope from a pendotite in Elliot Co , Ky Also, HzO = 10.
Ilia Theoretical composition of spessartite
Illb Spessartite from Amelia Court House, Va
IVa Theoretical composition of almandite
IVb Almandite from Sahda, Colo
Va Theoretical composition of andradite
Vb Andradite from East Rock, New Haven, Conn Also, HaO«.35.
Vc Schorlomite from Magnet Cove, Ark
VIft Theoretical composition of uvarovite
VIb Uvarovite from Bissersk, Urals
The crystals of garnet are usually simple combinations of oo 0(no)
(Fig. 166); 202(211) and often 301(321) (Figs 167 and 168), although
all the other holohedrons are also occasionally met with. Their cleavage
which is indistinct is parallel to oo 0(no).
310
DESCRIPTIVE MINERALOGY
When examined in polarized light many garnets, especially those
occurring in metamorphic rocks, are doubly refracting and, therefore,
have not the molecular structure belonging to isometric crystals This
FIG 166— Garnet Crystal. (Natural size ) Form ooQ (no)
FIG 167 FIG 168.
FIG 167— Garnet Crystals with coO, no (d) and 202, 211 (»),
FIG 168 —Garnet Crystal with d and n as in Fig 167 Also oo 02, 210 (<?) and 308
231 (s) '
phenomenon has been explained as due to several causes, the most rea-
sonable explanation ascribing it to strains produced in the crystals upon
cooling
ANHYDROUS ORTHOSILICATES 311
The garnets vary in color according to their composition, the com-
monest color being reddish brovin Their luster is Mtreous, their
streak white, hardness 6-7 5, and density 3 4-4 3 They are transparent
or translucent Most varieties are easily fusible to a light brown or
black glass, -which in the case of the varieties rich in iron is magnetic
U\ arovite, however, is almost infusible Some garnets are unattacked
by acids, others are partially decomposed
Garnets, when in crystals, are easily distinguished from other sim-
ilarly crystallizing substances by their color and hardness Massive
garnet may resemble tcsuuant'e, spkene, zircon or tzunnaine It is
distinguished from zircon by its easier fusibility and from vesuviarnte
by its more difficult fusibility, from tourmaline by its higher specific
gravity, and from sphene by the reaction from titanium
Under the influence of the air and moisture garnets may be partially
or entirely changed to epidote, muscovite, chlorite, serpentine, and oc-
casionally to other substances
Grossularite, Essomte, Hessonite, or Cinnamon Garnet occurs
principally in crystalline schists and in metamorphosed limestones,
where it is associated with other calcium silicates It is found also
in quartz ve;ns The mineral is white, bnght yellow, cinnamon-brown
or some pale shade of green or red. The lighter-colored varieties are
transparent or nearly so Those that are colored are used as gems
Much of the hyacvnfi of the jewelers is a red grossulante (seep 317)
Its hardness is about 7 and its density 3 4-3 6 It is fairly easily
fusible before the blowpipe. The refractive index of colorless vari-
eties for yellow light is, n= i 7438
Good crystals of grossulante occur at Phippsburg, Raymond and
Rumf ord, in Maine, and at many other places both in this country and
abroad Bright yellow varieties are reported from Canyon City, Colo
Pyrope is deep red, sometimes nearly black. Its hardness is a little
greater than 7 and its density 3 7 Its refractive index for yellow light
is between i 7412 and i 7504 The pure magnesium garnet is unknown
All pyropes contain admixtures of iron and calcium molecules Many
pyropes are transparent Those with a dark red color are used as gems
They occur principally in basic igneous rocks
The principal occurrence of the gem variety in this country is in
Utah, near the Arizona line, about 100 miles west of Ganado, Ariz ,
where it is found lying loose m wind-blown sand
Rhodolite is a pale rose-red or purple variety from Macon Co., N C
It consists of two parts pyrope and one of almandite.
312 DESCRIPTIVE MINERALOGY
Spessartite is hyacinth or brownish red, with occasionally a tinge
of violet The purest varieties are yellow, but since there is nearly
always an admixture of one of the iron molecules, the more usual color
is reddish brown The mineral is usually transparent Its hardness is
7 or a little greater, and its density 3 77-4 27 Its refractive index for
yellow light is i 8105 In the blowpipe flame it fuses fairly easily to a
black, nonmagnetic mass, and with borax gives an amethyst bead It
is found in acid igneous rocks and in various schists
Its best known occurrences in the United States are IP granite, at
Haddam, Conn , in pegmatite, at Amelia Court House, Va , and in
the lithophyse of rhyohtes, near Nathrop, in Colorado
Almandite is deep red, brownish red or black It is one of the com-
monest of all garnets It furnishes nearly all the material manufactured
into abrasives Transparent vaneties are also used as gems The min-
eral has a hardness of 7 and over Its density is 4 1-4 3, and its refrac-
tive index, n, for yellow light, is about i 8100 It is slightly decom-
posed by HC1 Before the blowpipe it fuses to a dark gray or black
magnetic mass It is found in granites and andesites, and also in various
gneisses and schists and in ore veins
Its best known occurrences in North America are at Yonkers and
at various points in the Adirondacks, N Y , at Avondale, Pa , and on the
Stickeen River, in Alaska
Andradite, or meknite, is black, brown, brownish red, green, brown-
ish yellow or topaz-yellow. The purest varieties are topaz-yellow or
light green and transparent The former constitute the gem topawhte
and the latter, demantwd The black variety, melamte, nearly always
contains titanium It occurs m alkaline igneous rocks, in serpentine,
in crystalline schists and in iron ores The most titamferous varieties
are known as schorlomtte The hardness of andradite is about 7 and its
density between 3 3 and 41 n for yellow light = i 8566 It is fusible
before the blowpipe to a black magnetic mass
The mineral is very widely spread It occurs at Franklin, N J , m
metamorphosed limestone, near Francoma, N H , in quartz veins, and
at many other places A black titamferous vanety occurs in a meta-
morphosed limestone in southwestern California and near Magnet Cove,
m Arkansas The vanety found at Magnet Cove is schorlormte It is a
black glassy mineral associated with brookite (TiCfe), nephdme (p 314),
and thomsomte (p 455)
Common garnet is a mixture of the grossularite, almandite and
ANHYDROUS ORTHOSILICATES 313
andradite molecules It occurs in many metamorphosed igneous rocks
and in some slates
Uvarovite is emerald-green It is rare, occurring only with chromite
in serpentine at Bissersk and Kyschtim in the Urals and in the chromite
mines at Texas, Penn , and New Idria, Cal Its hardness is about 7
and density 3 42 Its refractive index for yellow light is i 8384 It is
infusible before the blowpipe but dissolves in borax, producing a green
bead
Syntheses — Garnet crystals have been produced by fusing 9 parts of
nephelme and i part of augite (p 374) The fusion results in a
crystalline mass of nephelme, in which spinel and melamte crystals are
embedded
Occurrence — The members of the garnet group are widely spread in
nature They occur in schists, slates and other regionally metamor-
phosed rocks, in granite, rhyohte and other igneous rocks, and as con-
tact products in limestones They are found also in quartz veins, in
pegmatite, and associated with other silicates in ore veins. In some
instances they separated from a cooling magma, in others they are the
products of pneumatohtic process, and in others they are the results of
contact and dynamic metamorphism
Uses and Production — The varieties that are transparent are used
as gems Other varieties are crushed and employed as abrasives The
value of the gem material produced in the United States in 1912 was
$860 The production for abrasive purposes was 4,182 short tons, val-
ued at $137,800 All of this was produced in the mountain regions of
New York, New Hampshire and North Carolina The rock is crushed
and the garnet separated by hand picking, screening, or by jigging
The crushed material is used largely in the manufacture of garnet paper
NEPHELINE GROUP
The nephelme group of minerals includes three closely related com-
pounds, of which nepheline is the most common They are all alumino-
silicates of the alkalies Nephelme appears to be a solution of Si02,
or of albite, in isomorphous mixtures of the orthosilicates, NaAlSiO±
and KAlSiO* in the proportion of 8 molecules of the silicates to one of
Si02, thus
8(Na K)AlSi04+Si02=(Na K)0((Na- K) AlSi03)2Al6(Si04)7
The other two members of the group are eucryptite (LiAlSKX) and
kdhopkOOe (KAlSiQ*).
314 DESCRIPTIVE MINERALOGY
The members of the group crystallize in the hexagonal system and
are apparently holohedral, but nephelme is hemihedral and hemi-
morpmc (hexagonal pyramidal class) At temperatures above 1,248°
the nephelme molecule crystallizes also in the trichmc system as car-
negieite (see p. 418),
Nephelme
Although approximately a potash-soda silicate, nearly all specimens
of nephelme contain more or less CaO and nearly all contain small
quantities of water All contain an excess of SiCte To avoid the
necessity of assuming the existence of this SiCb m solution with
(Na K)AlSi04, it has been suggested that the variable composition of
the mineral may be explained by regarding it as a solid solution of
NaAlSisOg and CaAkS^Os (best known in their trichmc forms as
albite and anorthtte) in an isomorphous mixture of the two molecules,
NaAlSi04 and KAlSiO* The average of five analyses of crystals from
Monte Somma, Italy, is shown in I, and the composition of a mass of
the mineral from Litchfield, Maine, in II
Si02 A1203 CaO MgO Na20 KaO H20 Total
I 44 08 33 28 i 57 19 16 oo 4 76 15 100 03
II 43 74 34 48 tr tr 16 62 4 55 86 100 25
When found in crystals, the mineral is apparently holohedral in form
with an axial ratio i 8389 The crystals are nearly always short
columnar in habit and usually consist of very
simple combinations The most prominent
forms are ooP(ioTo), oop2(ii2o), oP(oooi),
2P(202l), P(lo7l), |P(loT2) and 2P2(lI2l)
(Fig 169) Their cleavage is imperfect parallel
toooP(ioIo) and oP(oooi)
Nephelme is glassy, white or gray and trans-
parent, when occurnng as implanted crystals
FIG i69--NepheUneCrys- The translucent va™*y with a glassy luster
tal with oP, oooi (c), *^a* occurs ln rocks is known as eleohte This
oo p, iolo (»), P, loir variety may be gray, pink, brown, yellowish or
(p) andoop2, 1120 (a) greenish The streak is always white The
fracture of both forms is conchoidal or uneven;
hardness, 5-6 and density, 2 6 For yellow light, co= 1.5424, €= i 5375.
ANHYDROUS ORTHOSILICATES 315
Before the blowpipe nephelme melts to a \\hite or colorless blebby
glass At 1,248° it passes over into carnegieite \\hich melts at 1,526°
It dissolves in hydrochloric acid with the production of gelatinous
silica Its powder before and after roasting reacts alkaline
The mineral is distinguished from other silicates by its crystalliza-
tion, gelatinization with acids, and hardness The massive varieties
are often distinguishable by their greasy luster
Nephelme alters to various hydrated compounds, especially to the
zeolites (p. 445), and to gibbsite, muscovite, cancnmte and sodahte
Syntheses — Nephelme has been prepared by fusing together AfeOa,
SiO2 and Na2C03, and by the treatment of muscovite by potassium
hydroxide.
Occurrence — The mineral occurs principally as an original constit-
uent of many igneous rocks, both plutomc and volcanic, and also as
crystals on walls of cavities in them
Locates —Crystals occur near Eberbach, in Baden, in the inclu-
sions within volcanic rocks at Lake Laach, in Rhenish Prussia, in the
older lavas of Monte Somma, Naples, Italy, at Capo de Bove, near
Rome, in southern Norway, and at various other points in southern
Europe Massive forms are found m coarse-brained rocks near Litch-
field, Maine, Red Hill, N H , Magnet Cove, Ark., m the Crazy Mts ,
Mont , and at other places
Cancrinite
Cancnmte is extremely complex in composition It is nearly allied
to nephelme but contains a notable quantity of C02 It corresponds
approximately to an hydrated admixture of Na2COs and 3NaAlSi04,
in which some of the Na is replaced by K and Ca Specimens from
Barkevik (I) in Norway, and from Litchfield (II), in Maine, yield the
following analyses:
Si02 AkOs Fe203 CaO Na20 K2O C02 EfeO Total
I 37 01 26 42 7 19 18 36 7 27 3 12 99 37
II. 36 29 30 12 tr. .4 27 19 56 18 6 96 2 98 100 36
Cancrinite is hexagonal (dihexagonal bipyramidal class).
Crystals are rare, and those that do exist are very simple, prismatic
forms bounded by ooP(ioTo), ooF2(ii2o), oP(oooi) and P(ioTi)
Their axial ratio is i : 4410
316 DESCRIPTIVE MINERALOGY
The mineral is usually found without crystal planes It is colorless,
white or some light shade, such as rose, bluish gray or yellow Its
streak is \vmte, its luster glassy, greasy or pearly and it is translucent
Its cleavage is perfect parallel to ooP(ioTo) and less perfect parallel
to oo P 2 1 1 20) Its break is uneven, hardness 5 and density 245
For red light* u>=i 5244? *=i 49S5
Before the blowpipe the mineral loses its color, swells and fuses to a
colorless blebby glass In the closed glass tube it loses CCb and water,
and becomes opaque After roasting it is easily attacked by weak
acids with effervescence and the production of gelatinous silica When
boiled with water Na2COs is extracted in sufficient quantity to give an
alkaline reaction
Cancrimte is easily distinguished by its effervescence with acids and
the production of gelatinous silica
Synthesis — Small colorless, hexagonal crystals with a composition
corresponding to that of cancnmte, have been made by treating mus-
covite with a solution of NaOH and NasCOs at 500°
Occurrence — The mineral occurs principally as an associate of neph-
elme in certain coarse-grained igneous rocks In some cases it appears
to be an original rock constituent and in others an alteration product of
nephelme It sometimes alters to natrohte (see p 454), foiming pseu-
domorphs
Localities — Cancrimte is found in rocks at Ditro, Hungary, at
Barkevik and other localities in southern Norway, where it occurs m
pegmatite dikes, m the parish of Kuolajarvi, in Finland, and in nephelme
syenite at Litchfield m Maine,
ZIRCON GROUP
The orthosihcates of zirconium, zircon, and of thorium, thorite, con-
stitute a group, the members of which possess forms that are almost
identical with those of rutile, cassitente and xenotime Indeed, parallel
growths of zircon and xenotime are not uncommon. Formerly zircon
was grouped with the two oxides.
Zircon and thorite are tetragonal (ditetragonal bipyramidal class),
with approximately the same axial ratios and the same pyramidal angles.
The two minerals are completely isomorphous
Zircon ZrSiO* a ' c= 6391 in A ill = 56° 37',
Thorite ThSi04 =6402 =56° 40'.
Zircon is fairly common Thorite is rare.
ANHYDROUS ORTHOSILICATES
317
Zircon (ZrSiO4)
Zircon, like rutile, is a fairly common compound of a comparatively
rare metal It is practically the only ore of the metal zirconium. It is
found mainly in crystals and as gravel
Although some specimens of zircon contain a large number of ele-
ments, others consist only of zirconium, silicon and oxygen in propor-
tions that correspond to the formula ZrSiO*, which demands 67 2 per
cent ZrO and 32 8 per cent SiOg
Its axial ratio is a : r=i ' 6301 Its crystals are usually simple
combinations of °o P(uo) and P(m), with the addition of oo P oo (100)
FIG 170
PIG 171
FIG. 170 — Zircon Crystals with «P, no (w), ooPoo, 100 (a), 3?, 331 («},
P, in (p) andsPs, 311 (x)
FIG 171 — Zircon Twinned about P <» (101) »=2P (221)
and often 3P3(3ii) (Fig 170) Elbow twins, like those of rutile and
cassitente, are known (Fig 171)
The cleavage of zircon is very indistinct. Its fracture is conchoidal.
Its hardness is 7.5 and density about 4 7 The mineral varies in tint
from colorless, through yellowish brown to reddish brown Its streak
is uncolored and luster adamantine Most varieties are opaque, but
transparent varieties are not uncommon The orange, brown and red-
dish transparent kinds constitute the gem known as hyacinth The
refractive indices for yellow light are* o>=i 9302, 6=1,9832.
Zircon is infusible, though colored varieties often lose their color
when strongly heated In the borax and other beads the mineral gives
no preceptible reactions. In fine powder it is decomposed by concen-
trated sulphuric acid. When fused with sodium carbonate on platinum
it is likewise decomposed, and the solution formed by dissolving the
fused mixture in dilute hydrochloric acid turns turmeric paper orange.
This is a characteristic test for the zirconium salts.
318 DESCRIPTIVE MINERALOGY
The mineral is easily recognized by its hardness, its resistance toward
reagents and its crystallization
Syntheses —Small crystals of zircon are obtained by heating for sev-
eral hours in a steam-tight platinum crucible a mixture of gelatinous
silica and gelatinous zirconium hydroxide Crystals have also been,
made by heating for a month a mixture of ZnCb and SiOa with 6 times
their weight of lithium bimolybdate
Occurrence and Ongin —Zircon is widely spread in tiny crystals as a
primary constituent in many rocks, and in large crystals in a few, notably
in limestone and a granite-like rock known as nephelme syenite In
limestone it is a product of contact action. It occurs also in sands,
more particularly in those of gold regions, and abundantly in a sand-
stone near Ashland, Va
Localities —The principal occurrences of the mineral are Ceylon, the
home of the gem hyacinth, the gold sands of Australia, Arendal,
Hakedal and other places in Norway; Litchfield and other points in
Maine, Diana, m Lewis Co , and a large number of other places in New
York, at Reading, Penn , Henderson and other Counties, m North
Carolina and Templeton, Ottawa Co , Quebec
Uses.— Zircon is the principal source of the zirconium oxide emplo)'ed
in the manufacture of gauze used in incandescent gas lights and in the
manufacture of cylinders for use in procuring a light from the oxyhydro-
gen jet. The mineral has been mined for these purposes in Henderson
Co , North Carolina
Transparent orange-colored zircons are sometimes used as gems
since they possess a high index of refraction and consequently have
a great deal of " fire " These are the true hyacinth The mineral
often called by this name among the jewelers is a yellowish brown
garnet
Production— k small quantity of zircon is usually obtained from
Henderson Co., N C , but it rarely amounts to more than a few hundred
pounds. The mineral occurs in a pegmatite and the soil overlying its
outcrop. It is obtained by crushing the rock and hand picking Usually
there is a little also separated from the sands in North Carolina and
South Carolina that are washed for monazite. A pegmatite dike, rich
in zircon, is also bemg prospected in the Wichita Mountains, Okla,, but
no mining has yet been attempted.
ANHYDROUS ORTHOSILICATES
319
Thorite (ThSiO4)
Thorite occurs in simple crystals bounded by ooP(no) and P(in)
(Fig 172), and in masses The mineral is always
more or less hydrated, but this is believed to be
due to partial weathering It is black or orange-
yellow (prangeite), has a hardness of 5 and a specific
gravity of 4 5-5 for black vaneties and 5 2-5 4 for
orange varieties Its streak is brown or light orange
Hydrated specimens are soluble in hydro chloric acid
with the production of gelatinous silica The min-
eral occurs as a constituent of the igneous rock,
augite-syemte, at several points m the neighborhood
of the Langesundfjord, Norway,
FIG 172 — Thonte
Crystal with oc P,
no (m) and P;
BASIC ORTHOSILICATES
ANDALUSITE GROUP
Three compounds with the empirical formula AkSiOs exist as min-
erals, kyamte, or disthene, andalusite and silhmanite. The first named is
less stable with reference to chemical agents than the other two, but at
high temperatures both kyamte and andalusite are transformed into
silhmanite Kyamte is regarded as a metasihcate (AlO^SiOa. The
other two are thought to be orthosilicates (Al(A10)SiC>4) The latter
are orthorhombic and both possess nearly equal prismatic angles
They differ markedly, however, in their optical and other physical
properties and, therefore, are different substances Kyamte is tnchnic
For this reason and because of its different composition it is not re-
garded as a member of the andalusite group A fourth mineral, topaz,
differs from andalusite in containing fluorine. Often this element is
present in sufficient quantity to replace all of the oxygen in the radical
(A1O) In other specimens the place of some of the fluorine is taken
by hydroxyl (OH). The general formula that represents these varia-
tions is A1(A1(F OH)2)Si04 The mineral crystallizes in forms that are
very like those of andalusite, and if corresponding pyramids are selected
as groundforms their axial ratios are nearly alike. Unfortunately,
however, different pyramids have been accepted as groundforms, and
therefore the similarity of the crystallization of the two minerals has
been somewhat obscured Daribunte, another mineral that crystallizes
m the orthorhombic system with a habit like that of topaz is often also
placed in this group, although it is a borosilicate, thus CaB2 (8104)2-
320
DESCRIPTIVE MINERALOGY
If 4P2(24i) be taken as the groundform of andalusite, 3^(331) as
that of topaz and 3? (331) as that of danbunte, the corresponding axial
ratios would be
Andalusite a b . c= 5069 i i 4246
Topaz = 5281 I * 43*3
Danbunte = 5445 * * 44°2
These, however, are not the accepted ratios, since other and more prom-
inent pyramids have been selected as the groundforms
Andalusite and Sillimanite (Al(AlO)SiO4)
Andalusite and sillimamte have the same empirical chemical compo-
sition and crystallize with the same symmetry, which is orthorhombic
holohedral (rhombic bipyramidal class), but they have different physical
properties and different crystal habits, and hence are regarded as dif-
ferent minerals The theoretical composition of both is
8102=3702,
Total= 16000
Nearly all specimens when analyzed show the presence of small
quantities of Fe, Mg, and Ca, but otherwise they correspond very closely
to the theoretical composition
Both minerals are characteristic of metamorphosed rocks, but
andalusite occurs principally in those that have been metamorphosed by
contact with igneous mtru-
sives, while Sillimanite is
especially characteristic of
crystalline schists and, in gen-
eral, of rocks that were dy-
namically metamorphosed It
also occurs with ohvme as in-
clusions in basalt lavas Silh-
FIG 173— Andalusite Crystals with oop, no mamte is more stable at high
(m), oP ooi (c), PS, oii w, cops, TOO temperatures than andalusite
(6), OOP 00,^010 (a), oo Pa, 210 (/), f^ *
120 (»), Poo, ioi (r), P, in (p) and
121 (*)
When m contact rocks it is
found nearer the intrusive
than andalusite
Andalusite— The accepted axial ratio of andalusite is 986*1 : i : 7024
Its crystals are columnar in habit and are usually simple combinations
Of 00 P 00 (IOO), 00 P 00 (OIO), OP(OOI), 00 P(lio), 00 P2(2IO), 00 P2(l2o)
Poo (ioi), Poo (on) with sometimes P (in) and 2P2(i2i) (Fig 173).
The angle no A 110=89° 12'
ANHYDROUS ORTHOSILICATES 321
The mineral, when fresh, is greenish or reddish and transparent
Usually, however, it is more or less altered, and is opaque, or, at most,
translucent, and gray, pink or violet Its cleavage is good parallel to
oo P(no) and its fracture uneven Its hardness is 7 or a little less and
its density 3 1-3 2 In some specimens pleochroism is marked, their
colors being olive-green for the ray vibrating parallel to a, oil-green for
that vibrating parallel to b and dark red for that vibrating parallel to c
For yellow light the indices of refraction are 01=16326, 1(3=16390,
7=1 6440
Before the blowpipe the mineral gradually changes to sillimamte and
is infusible When moistened with cobalt nitrate and roasted it becomes
blue It is insoluble in acids
The mineral is distinguished by its nearly square cross-section, its
hardness, its mfusibihty, and the reaction for Al, and by its manner of
occurrence in schists and metamorphosed slates
Some specimens contain as inclusions large quantities of a dark
gray or black material, which may be carbonaceous, arranged m
such a way as to give a cross-like figure in cross-sections of crystals.
Because of the shape of the figure exhibited by these crystals, this
variety was early called chiastohte, and was valued as a sacred
charm.
Andalusite alters readily to kaolin (p 404), muscovite (p 355), and
sillimamte It has not been produced artificially
Occurrence — Andalusite is found principally in clay slates and schists
that have been metamorphosed by contact with igneous masses, and
to a less extent m gneisses
Localities — Its principal occurrences are in Andalusia, Spain, at
Braunsdorf, Saxony, at Gefrees, in the Fichtelgebirge, in Minas
Geraes, Brazil, and m the United States at Standish, Maine, Westford,
Mass , and Litchfield, Conn Chiastohte occurs at Lancaster and
Sterling, Mass
Use — The only use to which andalusite has been put is as a semi-
precious stone, and for this purpose only the chiastolite variety is of any
value
SiUimanite, or fibrokte, occurs principally m acicular or fibrous
aggregates, on the individuals of which only the prismatic forms
ooP(no) and °oP|(23o) and the macropmacoid ooPw(ioo) can be
detected End faces are not sufficiently developed to warrant the
determination of an axial ratio The relative values of the a and b
axes are 687 : i. The angle iioAiio*8^0.
While most of the fibers correspond m composition very closely to the
322 DESCRIPTIVE MINERALOGY
theoretical value demanded by the formula Al(A10)Si04, many contain
small quantities of Fe20a, MgO and HkO
The mineral is yellowish gray, greenish gray, olive-green or brownish
It has a glassy or greasy luster and when pure is transparent Most
specimens, however, are translucent, and many of the colored varieties
show a pleochroism in brown or reddish tints Its cleavage is perfect
parallel to oo P 55 (100) Its needles have an uneven fracture trans-
versely to their long directions Their streak is colorless, hardness
6-7 and density 3 24 The mdices of refraction for the lighter colored
varieties are a=i 6603, j8= i 6612, 7— i 6818 for yellow light
Sillimanite reacts similarly to andalusite toward reagents and before
the blowpipe It is distinguished from other minerals by its habit and
manner of occurrence.
This mineral is much more resistant to weathering than is andalusite
It is, however, occasionally found altered to kaolin On the other hand,
it is known also in pseudomorphs after corundum
Synthesis —It has been produced b> cooling fused silicate solutions
rich in aluminium
Occurrence — Sillimanite is very widely spread in schistose rocks,
especially those that have been formed from sediments It is essentially
a product of dynamic metamorphism, but is formed also bv contact
metamorphism, m which case it is found near the intrusive, where the
temperature was high
Localities — Its principal occurrences in North America are in quartz
veins cutting gneisses at Chester, Conn , at many points in Delaware
Co , Penn , and at the Culsagee Mine, Macon Co , N C At the latter
place and at Media in Penn , a fibrous variety occurs m such large
masses as to constitute a schist — known as fibrohte schist.
Topaz (Al(Al(F-OH)2)Si04)
Topaz is a common constituent of many ore veins and is often present
on the walls of cracks and cavities in volcanic rocks It occurs massive
and also in distinct and handsome crystals
The mineral has a varying composition, which is explained in part
by the fact that it is a mixture of the two molecules Al(AlF2)SiO4 and
Al(Al(OH)2)SiOi The theoretical composition of the fluorine molecule
is 8102=32 6, A1203=SS 4, F=2o 7=108 7, deduct (0 = 2F)8 7
= loo.oo. A specimen from Florissant, Colo , gave.
F=i6 04=106 20-6 7s(0=F) = 99 45.
ANHYDROUS ORTHOSILICATES
323
Crystals of topaz appear to be orthorhombic (rhombic bipyramidal
class), but the fact that they are pyroelectnc and that they frequently
exhibit optical phenomena that are not in accord with the symmetry of
orthorhombic holohedrons suggests that they may possess a lower grade
of symmetry On the assumption that the mineral crystallizes with the
symmetry of orthorhombic holohedrons the axial ratio of fluorine varie-
ties is 5281 i 4771 l With the increasing presence of OH, however,
the relative length of a increases and that of c diminishes The angle
noAiTo=55° 43'-
The crystals are usually prismatic in habit with ooP(no) and
oo P?(i2o) predominating They are notable for the number of forms
FIG 174 FIG 175.
FIG 174 — Topaz Crystals with oo P, no (m), oo pT, 120 (Z), P, in (u), 2P, 221 (o)
4? oo , 041 00 and oo P oo , oio (6)
FIG 175 — Topaz Crystal with m, I, n and y as in Fig 174. Also 2? oo , 021 (/),
|P oo , 043 (*) and 2P 55 , 201 (d)
that have been observed on them, especially in the prismatic zone and
among the brachypyramids The number of the latter that have
already been identified is about 45
The three types of crystals that are most common are shown in
Figs 174, 175 and 176 Their most prominent forms are ooP(no),
ooP2(i2o), Poo (on), P(ni), |P(223), 4? ^(041), oo PJ (130) and
oP(ooi). Often planes are absent from one end of the vertical axis,
but since the etch figures on the prismatic planes do not indicate hemi-
morphism, the absence of the lacking planes is explained as being due to
unequal growth The planes of the prismatic zone are usually striated
The mineral is colorless, honey yellow, yellowish red, rose and rarely
bluish. When exposed to the sunlight the colored varieties fade, and
The more commonly accepted axial ratio is a : 6 : c-
£p(22i) 'being taken as the groundfonn*
5285 : i : .9539, the form
324
DESCRIPTIVE MINERALOGY
fj d, 0 and tt as m Figs 174 and 175
Also §P, 223 (z), oP, ooi (c) and
4P 55 , 401 (p)
when intensely heated some honey-yellow crystals turn rose-red Its
cleavage is perfect parallel to oP(ooi) and imperfect parallel to P 06 (on)
and P oo (101) The hardness of the mineral is 8 and its density 3 5-3 6
Its refractive indices for yellow light are a= i 6072, £= i 6104, 7= i 6176
for a variety containing very little OH, and 05=16294, £=16308,
7=16375 for a variety rich m
hydroxyl The indices of refraction
being high, the mineral when cut
exhibits much brilliancy — a feature
which, together with its hardness,
gives it much of its value as a
gem.
Topaz is infusible before the
blowpipe and is insoluble in acids
FIG 176— Topaz Crystal with m, I, y, At a high temperature it loses its
fluorine as silicon and aluminium
fluorides The mineral also ex-
hibits pyroelectncal properties, but
these are apparently distributed without regularity m different
crystals Many crystals contain inclusions of fluids containing bubbles,
and sometimes of two immiscible fluids the nature of which has not yet
been determined It has been thought that the principal fluid present
is liquid carbon-dioxide or some hydrocarbon
The mineral is distinguished from yellow quartz by its crystalliza-
tion, its greater hardness and its easy cleavage
Topaz is frequently found coated with a micaceous alteration product
which may be steatite (p 401), muscovite (p 355) or kaolin (p 404)
Synthesis — Crystals have been made by the action of hydrofluosihcic
acid (EfeSiFe) upon a mixture of silica and alumina m the presence of
water at a temperature of about 500°.
Occurrence — The mineral occurs principally in pegmatites, espe-
cially those containing cassitente, in gneisses, and in acid volcanic rocks
In all cases it is probably the result of the escape of fluorine-bearing
gases from cooling igneous magmas.
LocalMes —Topaz is found in handsome crystals at Schneckenstem
in Saxony, in a breccia made up of fragments of a tourmalme-quartz
rock cemented by topaz. It occurs also in the pegmatites of the tin
mines m Ehrenfnedersdorf, Marienberg and other places in Saxony,
Bohemia, England, etc , on the walls of cavities in a coarse granite m
Jekatennburg and the Hmengebirge, Russia, in veins of kaohn cutting
a talc schist in Mrnas Geraes in Brazil; and in the cassitente-bearmg
ANHYDROUS ORTHOSILICATES 325
sands at San Luis Potosi, Durango and other points in Mexico In the
United States it occurs on the walls of cavities m acid volcanic rocks, at
Nathrop, Colo , in the Thomas Range, Utah, and other places It occurs
also in veins Tilth muscovite, fluonte, diaspore and other minerals at
Stoneham, Maine, and Trumbull, Conn
Uses and Pi oduction — Topaz is used as a gem About 36 Ib , valued
at $2,675, was produced in the United States in 1911. In the following
year the production was valued at only $375.
Danburite (CaB2(Si04)2)
Danbunte, which is a comparatively rare mineral, is a calcium
borosilicate with the following theoretical composition 8102=4884,
B2Os = 28 39 and CaO= 2277 Usually, however, there are present in it
small quantities of AfeOs, Fe20s, MnaOs and EfeO Thus, crystals from
Russell, New York, contain
SiO2 B2O3 Al203,etc H20 CaO Total
49 70 25 80 i 02 20 23 26 99 98
The mineral crystallizes in the orthorhombic system (rhombic bipy-
ramidal class), with an axial ratio 5445 : i 4801 Its crystals are
usually prismatic in habit They contain a great number of forms, of
which oo P &> (100), oo P 06 (oio), co P2(i2o), oo P4(i4o), and oo P(iio)
among the prisms, 2P4(i42), 2P?(i2i) among
the pyramids and oP(ooi) are the most prom-
inent (Fig. 177). The angle iioAiib=
57° 8'.
When fresh and pure the mineral is trans-
parent, colorless or light yellow, but when
more or less impure is pink, honey-yellow or
dark brown Its streak is white, and luster
vitreous Its cleavage is imperfect parallel to JTIG I77 —Danbunte Cr>s-
oP(ooi) and its fracture uneven or conchoidal tal with oop, no (m),
Its hardness is about 7 and density 2 95-3 02 °°p2, 120 (Z), PSo , 101
Its refractive indices for vellow light are <«,«**,*« <r)"d4P-,
041 (w)
a=l 6317, 0=1 6337, 7=1 6383
Before the blowpipe the mineral fuses to a colorless glass and colors
the flame green It is only slightly attacked by hydrochloric acid, but
after roasting is decomposed with the formation of gelatinous silica.
It phosphoresces on heating, glowing with a red light.
Origin — Danburite is probably always a product of pneumatolytic
i
m
326 DESCRIPTIVE MINERALOGY
action, as it is found m quartz and pegmatite veins in the vicinity of
igneous rocks and on the walls of hollows within them
Locahtm —Its principal occurrences in this country are at Danbury,
Conn , where it is in a pegmatite, and at Russell, N Y , on the walls of
rocks and hollows in a granitic rock Its principal foreign occurrence is
at Piz Valatscha, in Switzerland.
EPIDOTE GROUP (CfcR'"i(OH)(Si(>4)i)
The epidote group comprises six substances, of which two are di-
morphs with the composition Ca2Al,3 (OH) (SiO^s = Ca2Al2(A10H) (SiO-Os
One of these, known as ztnstie, crystallizes in the orthorhombic system,
and the other, known as dinozoivite, m the monochiuc system The
other four are isomorphous with clmozoisite These are hancockite,
epidote, piedmontite and allanite The composition and comparative
axial ratios of the four commoner isomorphs are as follows (assuming
JP(Ti2) as the groundform of clmozoisite)
Clmozoisite Ca2 Ala (OH) (8104)3 i 4457 . i • i 8057
Epidote Ca*(Al Fe)8(OH)(Si04)s 15807 i i 8057, £=64° 36'
Piedmontite Ca2(Al Mn)s (OH) (8104)3 i 6100 i i 8326, 0= 64° 39'
Allaxute Ca2(Al Ce Fe)s (OH) (8104)3 i SS°9 J * 769*, 18=64° 59'
Clmozoisite is rare, though its molecule occurs abundantly m iso-
morphous mixtures with the corresponding iron molecule m epidote
Zoisite (Ca2Als(OH)(Si04)3)
Zoisite is a calcium, aluminium orthosilicate containing only a small
quantity of the corresponding iron molecule The theoretical composi-
tion of the pure Ca molecule is
810=3952, Al20s=3392> CaO=24$9, H20=i97 Total=ioooo
Colored varieties contain a little iron or manganese Green crystals (I),
from Ducktown, Tenn , and red crystals (thvtee) (II), from Kleppan, m
Norway, analyze as follows
Si02 A1203 Fe203 FeO CaO MgO Mn203 Na20 H20 Total
I 39 61 32 89 91 71 24 So 14 2 12 100 88
II 42,81 31 14 2 29 18 73 i 63 i 89 64 99 13
Zoisite crystallizes m the orthorhombic system (orthorhombic bi-
pyramidal class), with the axial ratio 6196 : i 3429. Its crystals are
ANHYDROUS ORTHOSILICATES
327
usually simple and without end faces The most frequent forms are
ooP(no), ooP4(i4o), oo P 06(010) P(in),2Pco(o2i)and4Po6(o4i)
are the commonest terminations (Fig 178) The crystals are all pris-
matic and are striated longitudinally Their
cleavage is perfect parallel to oo P 86 (oio)
The angle no A 110=63° 34'.
The mineral is ash-gray, yellowish gray,
greenish white, green or red in color and has a
white streak The rose-red variety, contain-
ing manganese, is known as thuhte Very
pure fresh zoisite is transparent, but the ordi-
nary forms of the mineral are translucent
Its luster is glassy, except on the cleavage
surface, where it is sometimes pearly Its
fracture is uneven Its hardness is 6 and
density about 33 In specimens from Duck-
town, Tenn , a=i 7002, /3=i 7025, 7=1 7058
for yellow light A notable fact in connection FIG 178— Zoisite Crystal
with this mineral is that with increase of the with*)?, no(»), ooPx,
molecule Ca2Fe3(OH)(Si04)3 in the mixture OIOJ6)» °°p4' ^ «>•
sPoo, 021 (it) and P, in
'
.*
the plane of its optical axes tends to change
from oP(oio) to oo P 06 (ooi)
Zoisite fuses to a clear glass before the blowpipe and gives off water,
which causes a bubbling on the edges of the heated fragments It is
only slightly affected by acids, but after heating it is decomposed by
hydrochloric acid with the production of gelatinous silica
Occurrence— The mineral occurs as a constituent of crystalline
schists, especially those rich in hornblende, or of quartz veins traversing
them It is also a component of the alteration product known as
saussitnte which results from the decomposition of the plagioclase
(p. 418) m certain basic, augitic rocks known as gabbros It is thus a
product of metamorphism
Localities — Good crystals of zoisite are found near Pregratten in
Tyrol, at Kleppan (thuhte), Parish Souland, Norway, and in the ore
veins at the copper mines of Ducktown, Tenn , where it is associated with
chalcopyrite, pynte and quartz.
Epidote (Ca2(Al-Fe)3(OH)(Si04)3)
Epidote, or pistazite, differs from the monochnic dimorph of zoisite
(dmozoisite) in containing an admixture of the corresponding iron sfli-
cate which is unknown as an independent mineral.
328 DESCRIPTIVE MINERALOGY
Since it consists of a mixture of an aluminium and an iron compound
its composition necessarily vanes The four lines of figures below give
the calculated composition of mixtures containing 15 per cent, 21 per
cent, 30 per cent and 40 per cent of the iron molecule
Per cent
Si02
A1203
Fe203
CaO
H2O
Total
38 60
28 80
6 65
24 02
i 93
100 00
38 23
26 76
9 32
23 78
i 91
100 00
37 67
23 71
13 3i
23 43
i 88
100 00
37 04
20 32
17 75
23 04
* 85
100 00
21
30
40
Most specimens contain small quantities of Mg, Fe, Mn, Na or K
Epidote is isomorphous with chnozoisite, crystallizing in the mono-
\
FIG 179— Epidote Crystals with °o P 55 , 100 (a), oP, 001(0), P w , 10! (r), |P 55 ,
102 (»), PI nI (») and P ob , on (0)
*FiG 180 — Epidote Crystals with a, c, r, *, wand 0 as m Fig 179 Also oop,
iio(w), 2PS6, 2oT(0, -P55, ioi W, -3?!, W (/O and JP5, 423 (/)
clime system (monochmc prismatic class), with the axial ratio i 5787 i
: 18036. #=64° 36'. The mineral is remarkable for its handsome
crystals, many of which are extremely rich in forms The crystals are
usually columnar in consequence of their elongation parallel to the b
axis The most prominent forms are oo P 56 (100), oP(ooi), ^P 56 (20!)
P w (jol), P(nl), oo P(no) and P 5b (on) (Fig, 179 and 180) In addi-
tion to these, over 300 other forms have been identified Twinning
is common, with oop^(ioo) the twinning plane The angle no A
ilo= 109° 56'.
Epidote is yellowish green, pistachio green, dark green, brown or,
rarely, red It is transparent or translucent and strongly pleochroic.
In green varieties the ray vibrating parallel to the b axis is brown, that
vibrating nearly parallel to c, yellow, and that vibrating perpendicular to
ANHYDROUS ORTHOSILICATES 329
the plane of these two is green Its luster is glassy and its streak gray
Its cleavage is very perfect parallel to oP(ooi) Its hardness is 6 5 and
density 3 3 to 3 5 The refractive indices for yellow light m a crystal
from Zillerthal are 05=17238, /5=i 7291, 7=1 7343 They increase
with the proportion of the iron molecule present, being i 7336, i 7593
and i 7710 :n a specimen containing 27 per cent of the iron epidote
The varieties that have been given distinct names are.
BucUwidite, a greenish black variety in crystals that are not elon-
gated,
Wtthanwte, a bright red variety containing a little MnO.
Fragments of the mineral when heated before the blowpipe yield
water and fuse to a dark brown or black mass that is often magnetic
With increase in iron fusion becomes more easy. Before fusion epidote
is practically insoluble in acid. After heating HC1 decomposes it with
the separation of gelatinous silica
The ordinary forms of the mineral are characterized by their yellow-
ish green color, ready fusibility and crystallization
Occurrence and Origin — Epidote occurs in massive veins cutting crys-
talline schists and igneous rocks, as isolated crystals and druses on the
walls of fissures through almost any rock and in any cavities that may
be in them, and as the pnncipal constituent of the rock known as epi-
dosite It is a common alteration product of the feldspars (p. 408),
pyroxenes (p 364), garnet, and other calcium and iron-bearing minerals
Pseudomorphs of epidote after these minerals are well known. The
mineral is a weathering product, but is more commonly a product of
contact and regional metamorphism.
It has not been produced artificially
Localities — Epidote crystals are so widely spread that only a few of
the important localities in which they have been found can be mentioned
here. Particularly fine crystals occur m the Sulzbachtibal, Salzburg,
Austria, in the Zillerthal, in Tyrol, near Zermatt, in Switzerland, in
the Alathal, Traversella, Italy, at Arendal, Norway, in Japan, at
Prince of Wales Island, Alaska, and at many other points in North
America
Piedmontite (Ca2(Al-Mn)3(OH)(SiO4)3)
Piedmontite is the manganese epidote, differing from the ordinary
epidote in possessing manganese in place of iron Usually, however,
the iron and the manganese molecules are both present. Typical analy-
ses of crystals from St. Marcel, in Piedmont, Italy (I), Otakisan, Japan
(II), and Pine Mt , near Monterey, Md (III), follow
330 DESCRIPTIVE MINERALOGY
Si02 A1203 Mn203 MnO Fe203 MgO CaO H20 Total
I 35 68 18 93 14 27 3 22 i 34 24 32 2 24 100 oo
II 36 16 22 52 6 43* 9 33 40 22 05 3 20 100 53*
III 47 37 18 ss 6 85 i 92 4 02 25 15 82 2 08 100 05*
* II contains also 44 per cent Na2<D The M^Oa contained also MnO
III contains also 2 03 per cent of the oxides of rare earths, 14 per cent PbO,
ii per cent CuO, 23 per cent Na.O and 68 per cent K^O The specimen contained
also a little admixed quartz which was determined with the SiOj
The axial ratio of piedmontite is i 6100 i . i 8326 18=64° 39'
Its crystals are similar m habit to those of epidote, but they are much
simpler The most prominent forms are oo P 60 (100), oP(ooi), P(In),
£P66(To2), ooP5b(oio) and ooP(no) Twins are fairly common,
with oo P 56 (too) the twinning plane.
The mineral is rose-red, brownish red or reddish black It is trans-
parent or translucent and strongly pleochroic in yellow and red tints
and has a glassy luster and pink streak It is brittle, and has a good
cleavage parallel to oP(ooi) Its hardness is 6 and density 3 40. Its
refractive indices are the same as those of epidote.
Before the blowpipe piedmontite melts to a blebby black glass and
gives the manganese reaction in the borax bead. It is unattacked by
acids until after heating, when it decomposes m HC1 with the separation
of gelatinous silica
It is characterized by its color and hardness and by its manganese
reaction
Occurrence and Origin — Piedmontite occurs as an essential constit-
uent of certain schistose rocks that are known as piedmontite schists
It occurs also m veins and m certain volcanic locks, where it is probably
an alteration product of feldspar. Its methods of origin are the same
as those of epidote
Localities — Good crystals are found in the manganese ore veins at
St. Marcel, Piedmont, on ilmenite in crystalline schists on the Isle of
Groix, off the south coast of Brittany, and at a number of points on the
Island of Shikoku, Japan, in crystalline schists and in ore veins In
the United States it is so abundant m the acid volcanic rocks of South
Mountain, Penn., as to give them a rose-red color.
Allanite (Ca2(Al-Ce-Fe)3(OH)(SiO4)3)
Allanite is a comparatively rare epidote m which there are present
notable quantities of Ce, Y, La, Di, Er and occasionally other of the
rarer elements Since cerium is present in the largest quantity the
ANHYDROUS ORTHOSILICATES 331
formula of the mineral is usually written as above, with the under-
standing that a portion of the cenum may be replaced by yttrium and
the other elements Some idea of the complex character of" the numeral
may be gained from the two analyses quoted below The first is of
crystals from Miask, Ural, and the second of a black massive variety
from Douglas Co , Colo
I II
Si02 30 81 31 13
Al20s 16 25 ii 44
Fe2O3 6 29 6 24
Ce2O3 10 13 12 50
BeO 27
Di203 3 43
La203 635
Y203 i 24
FeO 8 14 13 59
MnO 2 25 61
MgO 13 16
CaO 10 43 9 44
K20 53 tr
Na20 56
H20 2 79 2 78
C02 21
Total 98 77 99 8r
Allarute rarely occurs in crystals, but when these are found they are
usually more complex than those of piedmontite but much less compli-
cated than those of epidote. Their axial ratio is i 5509 : i : 1 7691
with £=64° 59' Their habit is like that of epidote crystals Common
forms are ooFco(ioo), oP(ooi), °°P(iio) Twins are like those of
epidote The mineral usually occurs as massive, granular or columnar
aggregates, or as ill-defined columnar crystals resembling rusty nails
It sometimes forms parallel mtergrowths with epidote.
It is black on a fresh fracture and rusty brown on exposed surfaces,
and has a greenish gray or brown streak It has a glassy luster and is
translucent in thin splinters, with greenish gray or brownish tints and
is pleochroic in various shades of brown Its hardness is 5-6 and
density 3-4, both varying with freshness and composition The cleav-
ages are imperfect and the fracture uneven Its indices of refraction
are nearly the same as those of epidote.
332 DESCRIPTIVE MINERALOGY
Small fragments of fresh allanite fuse to a blebby black magnetic
glass before the blowpipe and are decomposed by HC1 with the separa-
tion of gelatinous silica
Allamte is distinguished by its color, manner of occurrence, and the
reaction for water in the closed tube
The mineral alters readily on exposure to the weather, yielding
among other compounds mica and hmonite
Occurrence — Allanite occurs as an original constituent in some
granites, and other coarse-grained rocks It is found also in gneisses,
occasionally in volcanic rocks and rarely as a metamorphic mineral in
crystalline limestones
Localities — The best crystals have been found m the druses of a
volcanic rock at Lake Laach, Prussia, in coarse-grained granitic rocks
at several places in the Tyrol, in the limestone at Pargas, Finland, and
at various points in Ural, Russia Massive allanite occurs in the coarse
granite veins at Hittero, Norway and as the constituents of granites
at many places in the United States Parallel mtergrowths with epidote
are found in granite at Ilchester, Md
CHONDRODITE GROUP
The chondrodite group of minerals includes four members of the
general formula (Mg(F OH^Mg^SiO^y in which x equals i, 3, 5, 7, and
y, i, 2, 3, 4 Of these, one (humite) may be orthorhombic The other
three are monochmc with the angle £=90° The four members of the
group with their compositions and axial ratios are
0
Prolectite (Mg(F OH)2)Mg(Si04) i 0803 • i • i 8862 18=90'
Chondrodite (Mg(F OH)2)Mg3(SiO4)2 i 0863 i 3 1445 £=90
b Z
Humite (Mg(F OH)2)Mg5(Si04)3 i 0802 '1.4 4033
Clinohumtte (Mg(F OH)2)Mg7(Si04)4 r 0803 • i • 5 6588 £=90
To show the similarity in the ratios between the lateral axes of the
four minerals, the & axis of humite is written as i Chondrodite, humite
and clmohumite frequently occur together Chondrodite has been
reported at more localities than either humite or clmohumite, but it is
not certain that much of it is not chnohumite The three minerals
resemble one another very closely They are relatively unstable under
conditions prevailing at moderate depths in the earth's crust, passing
easily into serpentine, brucite or dolomite Only chondrodite is de-
scribed.
ANHYDROUS ORTHOSILICATES
333
Chondrodite (Mg3(Mg(F-OHJ2)(Si04)2)
Chondrodite is a rather uncommon mineral that occurs mainly as a
constituent of metamorphosed limestones that have been penetrated
by gases and water emanating from igneous rocks It is a characteris-
tic contact mineral
Its composition varies somewhat m consequence of the fact that OH
and F possess the power to mutually replace one another The two
analyses below are typical of varieties containing a maximum amount
of F
Si02 MgO FeO H20 F F=0 Total
I 33 77 57 98 3 96 * 37 5 14=102 22—2 16 100 06
II 35 42 54 22 5 72 9 00=104 36-3 78 100 58
I. Crystals from, limestone inclusions in the lava of Vesuvius
II. Grains separated from the limestone of the Tilly Foster Iron Mine, Brewster,
N Y
Chondrodite is monoclmic (prismatic class), with an axial ratio
i 0863 11:3 1445 18=90° The crystals vary widely in habit and
are often complex The forms oP(ooi),
oo P 66 (100), oo P oo (oio) and various unit
and clmohemipyramids of the general sym-
bol x?2 are frequently present, but other
forms are also common (Fig 181) Twin-
ning about oP(ooi) is also common
Usually, however, the mineral occurs m
little rounded grains, in some instances
showing crystal faces, scattered through FIG 181 —Chondrodite Crys-
hmestone tel ^ °P: ™ & » *** »
When fresh, Chondrodite has a glassy 1" ™v 2' "7 z£' * 2'
luster, is translucent and is white or has a _2p*2, 121 (r4)', — p, ni
light or dark yellow, brown or garnet color (j^), p, in (-«2);
It has a distinct cleavage parallel to oP(ooi),
a conchoidal fracture, a hardness of 6 and
a density of 3 15 Its refractive indices
for yellow light are: 01=1607, £=1619,
T= i 639
Before the blowpipe Chondrodite bleaches
without fusing With acids it decomposes with the production of
gelatinous silica
103 to)> jP°°7 ioi (— &)
and — P^, ioi (e%) The
a axis runs from right to left
and the upper left hand
octant is assumed to be
minus
334 DESCRIPTIVE MINERALOGY
It weathers readily to serpentine, chlorite and brucite, and conse-
quently many grams are colored dark green or black
Occurrence — Chondrodite, as has been stated, occurs in meta-
morphosed limestones It also occurs in sulphide ore bodies and m a
few instances in magnetite deposits It is probably in all cases a pneu-
matolytic or metamorphic product
Localities — It is found as crystals in the blocks enclosed m the lavas
of Vesuvius, in the copper mines of Kapveltorp, Sweden, in limestone
in the Parish of Pargas, Finland, and at the Tilly Foster Iron Mine, at
Brewster, N Y It occurs as grams in the crystalline limestone of
Sussex Co , N J , and Orange Co , N Y.
DATOLTTE GROUP
The members of the datolite group are four in number, but
of these only two, viz, datohte (Ca(B OH)Si04) and gadohnite
(Be2Fe(YO)2(Si04)2J are of sufficient importance to be described here
Both minerals crystallize similarly in the monoclmic system ('mono-
clinic prismatic class), with axial ratios that are nearly alike
Datolite a ' b c— 6345 i i 2657 ^ = 89° 51'
Gadohmte a b r= 6273 i 13215 ^ = 89°
Datohte (Ca(B OH)SiO4)
Datolite, or dathohte, is characteristically a vein mineral
The composition corresponding to the
formula given above is
= 218$; CaO=3Soo,
Total =100 oo
Some specimens contain a little AbO,* and
Fe20a but, m general, crystals that have
been analyzed give results that are m
close accord with the theoretical com-
FIG 182— Datohte Crystal wrth Positlon'
oo POO, zoo (a), OOP, no (m), The mineral crystallizes in fine crys-
-Poo, 101, (<£), — iPoo, 102 tals that are often very complicated (Fig
(*); -P, in (»), -P3, 212 ^2) About 115 different forms have
W, Poo, on (mv) and JPoo, been observed on ^^ Because of the
012 (g)
suppression of some faces by irregular
growth many of the crystals are columnar in habit, others are tabular.
Most crystals, however, are nearly equi-dimensional The angle
ANHYDROUS ORTHOSILlCATES 335
no /\ 1 10 -64° 40' The mineral occurs also in globular, radiating,
granular and massi\ e forms
Datohte is colorless or white, when pure, and transparent Often,
however, it is greenish, yellow, reddish or violet, and translucent. Its
streak is white and its luster glassy It has no distinct cleavage Its
fracture is conchoidal Its hardness is 5 and its sp gr about 3. Some
crystals are pyroelectnc For yellow light, a- 16246, 0=1.6527,
7=1 6694
Before the blowpipe it swells, and finally melts to a clear glass and,
at the same time, it colors the flame green Its powder before heating
reacts strongly alkaline. After heating this reaction is weaker. The
mineral loses water when strongly heated, and yields gelatinous silica
when treated with hydrochloric acid.
The mineral is characterized by its crystallization, its easy fusibility
and the flame reaction for boron
Synthesis — Datohte has not been produced artificially.
Occurrence, Origin and Localities — It occurs on the walls of clefts
in igneous rocks, in pegmatite veins and associated with metallic com-
pounds in ore veins. It is found in many ore deposits of pneumatolytic
ongin, notably at Andreasberg in the Harz Mts , at Markirch, in
Alsace, in the Seisser Alps, in Tyrol, in the Serra dei Zanchetti in the
Bolognese Apennines, at Arendal, Norway, and at many other places
In North Amenca it occurs at Deerfield, Mass , at Tariffville, Conn ,
at Bergen Hill, N J , and at several points in the copper districts of
the Lake Superior region
Gadolinite (Be2Fe(YO)2(Si04)2)
Gadolmite is a rather rare mineral with a composition that is not
well established Its occurrence is limited to coarse granite veins or
dikes — pegmatites — of which it is sometimes a constituent.
Its theoretical composition is as follows, on the assumption that it is
analogous to that of datolite
810=2556, Y203=4844, FeO=iS32; BeO=io68 Total=ioooo,
but nearly all specimens contain cermm oxides. Others contain nota-
ble quantities of erbium or lanthanum oxides and small quantities of
thorium oxide Nearly all show the presence of Fe20s, AfeOs, CaO and
MgO, and m some helium has been found
The mineral is found massive and in rough crystals with an axial
ratio a : b : c*= 6273 : i : i 3215 0=89° 26^'. The crystals show
comparatively few forms, of which ooP(no), oP(ooi), P£>(on),
336 DESCRIPTIVE MINERALOGY
JPob(oi2), P(Tn) and — P(in) are the most common The> are
usually columnar in habit and are lough and coarse The angle
iioA 110=64° 12'
Gadolmite is usually black or greenish black and opaque or trans-
lucent, but very thm splinters of fresh specimens are translucent or
transparent in green tints Its luster is glassy or resinous, streak
greenish gray and fracture conchoidal Its hardness is 6-7 and its
density about 4-4 5 Upon heating the density increases Many crys-
tals appear to be made up of isotropic and amsotropic substance, and
some to consist entirely of isotropic matter This phenomenon has
been explained in a number of different ways, but no one is entirely satis-
factory. In general, the isotropic material is believed to be an amor-
phous alteration form of the amsotropic variety It may be changed
into the amsotropic form by heating
The crystallized gadolmite swells up m the blowpipe flame without
becoming fused and retains its transparency The amorphous variety
also swells without melting, but yields a grayish green translucent mass
The mineral phosphoresces when heated to a temperature between that
of melting zinc and silver. After phosphorescing it is unattacked by
hydrochloric acid Before heating it gelatinizes with the same reagent
The mineral is weakly radioactive
Localities and, Origin — Gadolmite occurs in the pegmatites of Ytterby
near Stockholm, and of Fahlun, Sweden, on the Island of Hittero, in
southern Norway, in the Radauthal, in Harz, at Barringer Hill, Llano
Co , Texas, as nodular masses and large rough crystals, and at Devil's
Head, Douglas Co, Colo In the last locality it occurs in a de-
composed granite as a black isotropic variety with a very complex
composition Specimens analyzed as follows
I H
Si02 22 13 21 86
Th02 89 81
AbOs 2 34 54
Fe20a i 13 3 S9
ii 10 6 87
(La Di)20a 21 23 19 10
Y20g . 9 50 12 63
ErgOs . , ,. 12.74 15 80
I
FeO 10 43
BeO 7 19
CaO 34
H20 . 86
Other 60
Total , , 100 48 100 02
It has apparently in some cases solidified from an igneous magma.
In others it is of pneumatolytic origin
ANHYDROUS ORTHOSILICATES
337
StauroUte (Fe(AlOH)(A10)4(Si04)2)
Staurolite is a mineral that is interesting from the fact that it fre-
quently forms twinned crystals that resemble a cross in shape, and which
consequently, during the Middle Ages, was held in great veneration
Its composition is not well established The composition indicated by
the formula above is as shown in the first line below (I) Three analyses
are quoted in the next three lines
A1203
Fe203
FeO
MgO
H20
55 9
158
2 00
54 20
6 83
Q 13
i 43
51 16
14 66
2 73
i 26
52 92
6 87
7 80
3 28
1 59
Total
100 oo
98 97
loo 33
100 37
SiOo A1203 Fe203 FeO MgO H20 Ti02
I 26 3
II 27 38
HI 30 23
IV 27 91
I Theoretical composition
II From Monte Campione, Switzerland
III From Morbihan, France
IV From Chesterfield, Mass
Staurolite crystallizes in the orthorhombic system (bipyramidal
class) in simple crystals with the axial ratio 4734 * i : 6828 The indi-
FIG 183 FIG 184 FIG 185
FIG 183 — Staurolite Crystal with ooP, no (ni), oopoo, 100 (&), oP, ooi (c) and
P 60,101 (r)
FIG 184 — Staurohte Crystal Twinned about |P oo (032)
FIG 185 —Staurolite Crystal Twinned about |P} (232)
vidual crystals are usually bounded by oo P(no), oo P 65 (ooi), P 55 (101)
and often oP(ooi), but all their faces are rough (Fig 183) The angle
1 10 A i io =50° 40' More common, however, than the simple crystals
are interpenetration twins The most common of these are of two kinds,
(i) with f P 06 (032) the twinning plane (Fig 184), and (2) with |P|(232)
the twinning plane (Fig. 185) Both types of twins yield crosses, but
the arms of the first type are perpendicular to one another and those of
338 DESCRIPTIVE MINERALOGY
the second type make angles of about 60° and 120° Sometimes the
twinning is repeated, giving rise to trillings
The mineral is reddish or blackish brown, and has a glassy or greasy
luster. Its streak is white It is slightly translucent in fresh crystals,
but usually is opaque In very thin pieces it is pleochroic in hyacinth-
red and golden yellow tints Its cleavage is distinct parallel to oo P 06
(oio) and indistinct parallel to ooP(no) Its fracture is conchoidal,
its hardness 7 and its density 34~38 For yellow light, QJ=I 736,
/3=i 741, 7= i 746
Before the blowpipe staurohte is infusible, unless it contains man-
ganese, in which case it fuses to a black magnetic glass It is only
slightly attacked by sulphuric acid
It is distinguished from other minerals by its crystallization, m-
fusibility and hardness
Staurolite weathers fairly readily into micaceous minerals, such as
chlorite (p 428) and muscovite (p. 355)
Synthesis — It has not been produced in the laboratory
Occurrence — The mineral occurs principal!} m mica schist and other
schistose rocks where it is the result of regional or contact metamor-
phism Because of its method of occurrence it frequently contains
numerous mineral inclusions, among them garnet and mica
Localities — Good crystals of staurohte are found in the schists at
Mte Campione, Switzerland, in the Zillerthal, Tyrol, at Aschaff en-
burg, in Bavana, at various places in Brittany, France, and in the
United States, at Wmdham, Maine, at Francoma, N H , at Chester-
field, Mass , in Patrick Co , Va , and m Fannm Co , N C
Uses — Twins of staurohte are used, to a slight extent, as jewelry.
Specimens from Patrick Co , Virginia, are mounted and worn as charms
under the name of " Fairy Stones."
Dumortierite (Al(AlO)7H(BO)(SiOi)3)
Dumortierite is one of the few blue silicates known It is a borosili-
cate with a composition approaching the formula indicated above The
analysis of a sample from Clip, Arizona, gave (I)
SiO2 AbOs Fe203 Ti^Oa MgO B203 P20r> Lossonlgn Total
I. 27 99 64 49 tr 4 95 20 i 72 99 35
II. 28 58 63 31 21 i 49 5 2i r 53 ioo 33
Specimens from California (II) contain in addition notable quantities
of TiCfe, which is thought to exist as Ti203 replacing a part of the AkOa.
ANHYDROUS ORTHOSILICATES 339
The mineral crystallizes in the orthorhombic s>stem in aggregates of
fibers, needles or very thin prisms exhibiting only ooP(no) and
oo P oo (100) without end faces Its axial ratio is a . b= 5317 : i, and
the prismatic angle no A 110=56° Its crystals possess a distinct
cleavage parallel to oo P 66 (100) and a fracture perpendicular to the
long axes of the prisms Twinning is common, ^ith ooP(no) the
twinning plane
Dumortierite is commonly some shade of blue, but in some cases is
green, lavender, white, or colorless It is translucent or transparent
and strongly pleochroic, being colorless and red, purple or blue Its
streak is light blue Hardness is 7 and density 3 3 Its refractive indices
for yellow light are a= r 678, /3= i 686, 7= i 089
Before the blowpipe the mineral loses its color and is infusible. It is
insoluble m acids
It is distinguished from other blue silicates by its fibrous or columnar
character and its insolubility m acids
Its principal alteration products are kaolin and damourite
(pp 404, 357)
Occurrence and Locates — Dumortierite occurs only as a constit-
uent of gneisses and pegmatites It is found in pegmatite near Lyons,
France, near Schmiedeberg, m Silesia, at Harlem, N Y, in a granular
quartz, at Clip, Yuma Co , Ariz , and in a dike rock composed of quartz
and dumortiente, near Dehesa, San Diego Co , Cal It is evidently
a pneumatolytic mineral Its common associates are kyamte, anda-
lusite or sillimanite
SODALITE GROUP
The sodahte group includes a series of isometric minerals that may be
regarded as compounds of silicates with a sulphate, a sulphide or a chlor-
ide, or, perhaps better, as silicates in which are present radicals con-
taining Cl, SO4 and S The minerals comprising the group are hauymte,
nosean, sodalite and lasnnte* Of these, sodahte appears to be a mixture
of 3NaAlSiO4 and NaCl, in which the Cl has combined with one atom of
Al, thus Na4(ClAl)Al2(SiC>4)3 The other members of the group are
comparable with this on the assumption that the Cl atom is replaced by
the radicals NaS04, and NaSa It is possible, however, that all are
molecular compounds as indicated by the second set of formulas given
below. All are essentially sodium salts, except that in typical haiiynite
a portion of the Na is replaced by Ca. The chemical symbols of the
four minerals with the calculated percentages of silica, alumina and
soda corresponding to their formulas are:
340
DESCRIPTIVE MINERALOGY
Si02 A1203 Na20
37 14 31 60 25 60
31 65 27 03 27 26
Sodalite Na4(Cl • Al) Al2(Si04)3, or
3NaAlSi04 NaCl
Noselite Na4(NaSQi Al)Al2(Si04)3, 01
3NaAlSi04 Na2S04
Hauymte (Na2Ca)2(NaSOrAl)Ab(SiO1)3, or 3199 2732 16.53
3NaAlSi04 CaSO4
Lasurxte Na4(NaS3 Al) A12 (8104)3, or 31,7 26,9 27.3
Na2S S*
Sodalite
A1)A12 (8104)3)
Sodalite, theoretically, is the pure sodium compound corresponding
to the composition indicated by the formula given above Natural
crystals, however, usually contain a little potassium in place of some of
the sodium and often some calcium, as indicated by the analyses of
material from Montreal, Canada (I), and Litchfield, Maine (II), quoted
below Moreover, their content of Cl is not constant
Si02 A1203 Na20 K2OCaO Cl C1«O Total
I 3752 3*38 2515 78 35 691 - 10209 -155 10054
II 3733 3187 2456 10 . 683 = 10176* -154 10022
* Includes I 07 per cent H20
Sodalite occurs massive and in crystals that appear to be holohedral,
but etch figures indicate that they are probably tetrahedrally hemi-
hedral (hextetrahedral class) Most crystals
are dodecahedral m habit, though some are
tetrahexahedral and others octahedral The
forms usually developed are ooO(no),
ooQoo (100), 0(iu), 202(112) and 404(114).
Interpenetration twins of two dodecahedrons
are common, with 0 the twinning plane (Fig
186) These often possess an hexagonal habit,
The mineral is colorless, white or some
light shade of blue or red, and its streak is
white Its luster is vitreous It is trans-
parent, translucent and sometimes opaque
Its cleavage is perfect parallel to ooO(no)
and its fracture conchoidal Its hardness is 5-5,6, and its density
2 3. Its refractive index for yellow light, n= 14827 Some specimens
are distinctly fluorescent and phosphorescent.
FIG 186— Sodalite Inter-
penetration Twin of Two
Dodecahedrons Elon-
gated in the Direction of
an Octahedral Axis and
Twinned about 0(m)
ANHYDROUS ORTHOSILICATES 341
Before the blowpipe, colored varieties bleach and all varieties swell
and fuse readily to a colorless blebby glass The mineral dissolves com-
pletely in strong acids and yields gelatinous silica, especially after heat-
ing When dissolved in dilute nitric acid its solution yields a chlorine
precipitate with siher nitrate Its powder becomes bro\\n on treatment
with AgNOs, in consequence of the production of AgCl
The mineral is best distinguished from other similarly appearing
minerals by the production of gelatinous silica with acids and the reac-
tion for chlorine
As a result of weathering sodahte loses Cl and Na and gams water
Its commonest alteration products are zeolites (p 445), kaolin (p 440),
and muscovite (p 355)
Syntheses — It has been produced artificially by dissolving nepheline
ponder in fused sodium chloride, and by decomposing muscovite
with sodium hydroxide and NaCl at a temperature of 500° C
Occurrence and Ortgm — Sodahte occurs principally as a constituent
of igneous rocks rich in alkalies and as crystals on the walls of pores in
some lavas It is also known as an alteration product of nephehne
Localities — Good crystals are found in nepheline syenite at Ditro,
in Hungary, in the lavas of Mte Somma, Italy, in the pegmatites of
southern Norway; and at many other points where nephehne rocks
occur In North America it is abundant in the rocks at Brome, near
Montreal, in the Crazy Mts , Montana, and at Litchfield, Maine The
material at the last-named locality is light blue
Noselite and Haiiymte ((Na^CaHNaSCX Al)Al2(Si04)3)
Noselite, or nosean, and hauynite, or hauyn, consist of isomorphous
mixtures of sodium and calcium molecules of the general formula given
above Those mixtures containing a small quantity of calcium are
usually called nosean, while those with larger amounts constitute hauyn.
The theoretical nosean and hauyn molecules are indicated on p 340
The theoretical compositions of the pure nosean molecule (I) and of the
most common hauyn mixture (II) are as follows
SiO2 A1203 Fe203 CaO Na20 Ka20 S03 H20 Total
I 31 65 27 03 27 26 14 06 100 oo
II 31 99 27 32 9 94 16 53 14 22 100 oo
HI 35 99 29 41 31 21 20 91 10 58 i 63 99 61
IV 33 78 27 42 10 08 13 26 3 23 12 31 . 100 08
* Contains also 57 per cent Cl
342 DESCRIPTIVE MINERALOGY
In line III is the analysis of a blue nosean from Siderao, Cape Verde,
and in line IV, the analysis of a blue haiiyn from the lava of Monte Vul-
ture, near Melfi, Italy
Nosean and hauyn are isomorphous with sodalite They crystallize
is the isometric system in simple combinations with a dodecahedral
habit The principal forms observed aie ooO(no), ooOoo(ioo)
0002(102), 0(in) and 202(112) Contact and mterpcnetration twins
are common, with 0(m) the twinning plane The twins are often
columnar.
The minerals have a glassy or greasy luster, are transparent or trans-
lucent, have a distinct cleavage parallel to ooQ(iio) and an uneven or
conchoidal fracture Their hardness is 5 6 and density 2 25 to 2 5, the
value increasing with the amount of CaO present Nosean is generally
gray and hauyn blue, but both minerals may possess almost any color,
from -white through light green and blue tints to black Red colors are
rare The streaks of both minerals are colorless, or bluish For yel-
low, light #=14890 to i 5038, increasing with increase m the Ca
present Both minerals are fluorescent and phosphorescent.
Before the blowpipe both minerals fuse with difficulty to a blebby
white glass, the blue hauyn retaining its color until a high temperature
is reached In this respect it differs from blue sodalite which bleaches
at comparatively low temperatures Upon treatment with hot water
both minerals yield NaaS04 They are decomposed with acids yielding
gelatinous silica The powders of both minerals react alkaline Both
also give the sulphur reaction with soda on charcoal
The minerals are easily distinguished from all others by their crys-
tallization, gelatmization with acids and reaction for sulphur.
Both minerals upon weathering yield kaolin or zeolites and
calcite
Synthesis — Crystals of nosehte have been made by melting together
Na2C03, kaolmite and a large excess of Na2SO*
Occurrence — Hauyn and nosean occur in many rocks containing
nephehne, especially those of volcanic origin and m a few metamorphic
rocks. Hauyn is so common m some of them as to constitute an essen-
tial component
Localities — Both minerals are found in good crystals in metamor-
phosed inclusions in the volcanic rocks of the Lake Laach region, in
Prussia, also in the rocks of the Kaiserstuhl, m Baden, in those of
the Albanian Hills, in Italy, and at S. Antao in Cape Verde In
America haiiyn has been reported from the nephelme rocks of the
Crazy Mts,, Montana,
ANHYDROUS ORTHOSILICATES 343
Lasunte (Na4(NaS3- Al)Al2(Si04)3)
Lasunte is better known as lapis lazuli It is bright blue in color
and was formerly much used as a gem stone The material utilized for
gem purposes is usually a mixture of different minerals, but its blue
color is given it by a substance with a composition corresponding to the
formula indicated above Since the artificial ultramarine, which is
ground and used as a pigment, also has this composition, the molecule is
sometimes represented by the shortened symbol USs, or if it contains
but two atoms of S, by the symbol US2 The deep blue lasunte from
Asia contains as its coloring material a substance with a composition
that may be represented by 15 7 molecules of USs, 76 9 molecules of
hauyn and 7 4 molecules of sodahte, corresponding to the percentages.
SiO2 A1203 CaO Na20 K20
32 52 27 61 6 47 19 45 28
S03 S Cl Total (Less C1 = O)
10 46 2 71 47 99 97 = 99 42
Lasunte is thus the name given to the blue coloring matter of lapis
lazuli, which is a mixture It apparently crystallizes in dodecahedrons
Its streak is blue, its cleavage is dodecahedral, its hardness about 5 and
its specific gravity about 2 4 Before the blowpipe it fuses to a white
glass Its powder bleaches rapidly in hydrochloric acid, decomposes
with the production of gelatinous silica and yields H2S.
It is distinguished from blue sodalite and hauyn by the reaction with
HC1, especially by the evolution of H2S
Occurrence — Lasunte is principally a contact mineral in limestone.
Localities — Good lapis lazuli occurs at the end of Lake Baikal, in
Siberia, in the Andes of Ovalle, in Chile, in the limestone inclusions in
the lavas of Vesuvius, and in the Albanian Mts , Italy
Uses — Lapis lazuli is used as an ornamental stone in the manufacture
of vases, and various ornaments, in the manufacture of mosaics, and as a
pigment, when ground, under the name ultramarine Most of tfre ultra-
marine at present in use, however, is artificially prepared,
ACID ORTHOSILICATES
Prehaite (H2Ca2Al2(SiO4)3)
Prehmte is nearly always found in crystals, though it occurs also in
stalactitic and granular masses
The theoretical composition of the pure mineral is 8102=43.69,
344 DESCRIPTIVE MINERALOGY
A1203=>2478, CaO=27i6, and H2O = 437 Most crystals, however,
contain small quantities of FeoOj and other constituents
SiQ. AUOi I'cjOj KO CaO M«0 II.O Total
Jordansmuhl, Silesia 44" 26 °° Al 2<> 2° tr 49* 10090
Cornwall, Penn 4^ 4Q 20 88 5 54 27 o^ ti 4 or 99 85
Chlorastrohte, Isle Royale 37 41 H 02 2 21 i 81 22 20 3 46 7 72 99 75*
* Also 32 per cent Na^O
Its crystallization is orthoihomhic and hcraimoiphic (rhombic py-
ramidal class), with a b c= 8420 i i 1272 The ciystals vary
widely in habit, but they contain comparatively few foinis The most
prominent are oP(ooi), ooP(uo), 6P»(o6i), 2P(32i) and 6P(66i)
(Fig 187) The angle noAiTo=8o°
12' Because they exhibit pyroelectnc
l>olanty in the direction of the a a.xis the
crvstals arc thought to be twins, with
FIG 187 — Prehnite Crystal with * _ _ / N . , , .
OOP/XXO W, OOP/, I0o Wl «P» (I*) as the twinning plane
JP56, 304 (n), JP55, 308 W Cleavage is good parallel to oP(oor)
and oP, ooi (c) The crystals are frequently tabular
parallel to oP(ooi), although other
habits are also common Isolated individuals are rare, usually many
are grouped together into knotty or warty aggregates
Prehnite is colorless or light green, and transparent or trans-
lucent, and it has a colorless streak Its luster is pearly on oP(ooi) but
glassy on other faces Its fracture is uneven, its hardness 7+ and its
density 2.80-2 95. For yellow light, a= i 616, 0= i 626, 7 = 1 649
Before the blowpipe prehnite exfoliates, bleaches and melts to a
yellowish enamel At a high temperature it yields water Its powder is
strongly alkaline. It is partially decomposed by strong hydrochloric
acid with the production of pulverulent silica. After fusion it dissolves
readily in this acid yielding gelatinous silica
The mineral has not been produced artificially
Occurrence — Prehnite occurs as crystals implanted on the walls of
clefts in siliceous rocks, in the gas cavities in lavas, and in the gangue of
certain ores, especially copper ores It is found also as pseudomorphs
after analcite (p 438), laumomte (p 451), and xutrohte (p 454) In
all cases it is probably a secondary product •
Localities — Fine crystals come from veins at Harzburg, in Thuringia,
at Stnegau and Jordansmuhl, Silesia, and at Fassa and other places in
Tyrol. Good crystals are found also in the Campsie Hills in Scotland.
The mineral is abundant in veins with copper along the north shore of
ANHYDROUS ORTHOSILICATES 345
Lake Superior and on Keweenaw Point, and it occurs also at Farmington,
Conn , Bergen Hill, N J , and Cornwall, Penn
Uses — The mineral known as chlorastrolite is probably an impure
prehnite. It is found on the beaches of Isle Royale and the north shore
of Lake Superior as little pebbles composed of stellar and radial bunches
of bluish green fibers The pebbles were originally the fillings of gas
cavities in old lavas The> are polished and used, to a slight extent, as
gem-stones About $2,000 worth were sold in 1911 and §350 ^orth in
1912
Axinite (H(Ca-Fe-Mn)3Al2B(SiO4)4)
Axmite is especially noteworthy for its richness in crystal forms
The mineral is a complicated borosihcate for ^vhich the formula given
above is merely suggestive Analyses of crystals from different localities
vary so widely that no satisfactory simple formula has been proposed
for the mineral Four recent analyses are quoted below
Radauthal Stnegau Oisans Cornwall
Si02 39 26 42 02 41 53 42 10
A12O3
FeoOs
FeO
MnO
CaO
MgO
H2O
4 gi
£ OO
4 62
4 64
14 46
17 73
17 90
17 40
2 62
93
3 9°
306
365
65S
4 02
5 84
2 80
6 52
3 79
4 63
29 70
19 21
21 66
20 53
2 00
38
74
66
I 22
i 77
2 l6
i 80
Total 100 62 ico ii 100 32 100 66
Axinite crystallizes in the trichmc system (pinacoidal class), with
a : b : c=* 4921 . i : 4797 and 01=82 ° 54', 0=91° 52', 7=i3l0 32'-
The crystals are extremely varied m habit but nearly all are somewhat
tabular parallel to 'P(iTi), oo P'(iio) or oo 'P(iTo) About 45 forms
have been observed In addition to the three mentioned, 2'?' So (201),
P'(III), /P(iFi), 2yP' 06 (021), oo P 06 (oio) and oo P oo (100) are the most
frequently met with (Figs 188, 189) The plane 'P(iTi) is usually
striated parallel to its intersection with oo 'P(iTo) The angle 100 A i "10
= 15° 34'. The cleavage is indistinct parallel to ooP'(no) and the
crystals are strongly pyro electric
Axinite is brownish, gray, green, bluish or pink, and is strongly pleo-
chroic in pearl-gray, olive-green and cinnamon-brown tints It is
346 DESCRIPTIVE MINERALOGY
transparent or translucent and has a glassy luster and a colorless streak
Its fracture is conchoidal or uneven It is brittle, has a hardness of 6-7
and a density of 3 3 For red light, a= i 6720, /3= i 6779, 7 = 1 6810
Axmite, before the blowpipe, exfoliates and fuses to a dark green
glass which becomes black in the oxidizing flame It colors the flame
green, especially upon the addition of KHS04 and CaFo to its powder
Its powder reacts alkaline It is only slightly attacked by acids. After
FIG 188 FIG 189
FIG 188— Aximte Crystal with ooPoo, TOO (a), 2'P'So, 201 (s), ooP/, no (m),
oo /p ilo (M), P', m (*) and 'P, ill (r)
FIG 189 — Axmite Crystal with M , m, a, r and 5 as m Fig 188 Also ooPoo,
oio (6), aP' w , 021 (v), yP, In (e), |,P3, 132 (0), 4/P^, 241 (o), 3/P3, 131 (I'),
00 /'PI. 130 (w), 3'P3, i3i (») and 4'?% 241 (<J).
fusion, however, it dissolves readily with the production of gelatinous
silica
The mineral is easily characterized by its crystallization and the
green color it imparts to the flame
It has not been produced artificially
Pseudormorphs of chlorite after axroite have been found in Dart-
moor, England
Occurrence — Axmite crystals occur in cracks in old siliceous rocks.
It is found also in ore veins and as a component of a contact rock com-
posed mainly of augite, hornblende and quartz, occuning near the
peripheries of granite and diabase masses. It was formed by the aid
of pneumatolytic processes
Localities — Excellent crystals of axmite are found at Andreasberg
and other places in the Harz Mts , near Stnegau, m Silesia, near
Poloma, in Hungary, at the Piz Valatscha, in Switzerland, near Verms
and at other points m Dauphme, France, at Botallak, Cornwall, Eng-
land, at Komgsberg, Norway, Nordmark, Sweden; Lake Onega, and
Miask, Russia, at Wales in Maine and at South Bethlehem, Penn.
ANHYDROUS ORTHOSILICATES 347
Dioptase (H2CuSiO4)
Dioptase is especially interesting because of its crystallization, which
is rhombohedral tetartohedral (trigonal rhombohedral class) Its crys-
tals are columnar Their axial ratio is i 5342 They are usually
bounded by oo P2(ii2o), - 2R(o22i) or R(ioYi) and ~^i - (1341) or
jT> JL Y 4 ^
H - (3141) (a rhombohedron of the third order, Fig 190) Besides
occurring as crystals the mineral is found also
massive and in crystalline aggregates.
The composition expressed by the formula
given above is 8102—3818, CuO=504o;
H20=n 44, which is approached very closely
by some analyses. The same composition may
be expressed by CuSiOs HaO Indeed, recent
work indicates that the mineral is a hydrated
metasilicate and not an acid orthosihcate FIG 190 —Dioptase Ciys-
Dioptase has an emerald-green or blackish tai Wlth °°P2» "20 and
green color, a glassy luster and a green streak ~~2R' °221 ®> mtl[L a
It is transparent or translucent, is brittle
and its fracture is uneven or conchoidal Its stnations
hardness is 5 and its density 3 05. It is weakly
pleochroic and is distinctly pyroelectnc For yellow light, co=i 6580,
6=17079
Before tie blowpipe dioptase turns black and colors the flame green.
On charcoal it turns black in the oxidizing flame and red m the reducing
flame without fusing It is decomposed by acids with the production of
gelatinous silica
Synthesis — Crystals of dioptase have been made by allowing mix-
tures of copper nitrate and potassium silicate to diffuse through a sheet
of parchment paper
Occurrence and Localities — The mineral occurs in druses on quartz
in clefts in limestone, and in gold-bearing placers in the Altyn-Tube Mt.
near the Altyn Ssu River, m Siberia, in crystals on wulfemte and cala-
mme and embedded in clay near R6zbanya, Hungary, with quartz and
chrysocolla in the Mmdonli Mine, French Congo, in copper mines at
Capiapo, Chile, and in Peru, at the Bon Ton Mines, Graham Co ,
Ariz , and near Riverside, Pinal Co,, in the same State. In the Bon
Ton Mines it covers the walls of cavities in the ore, which consists of a
mixture of kmomte and copper oxides
348
DESCRIPTIVE MINERALOGY
MICA GROUP
The mica group comprises a series of silicates that are characterized
by such perfect cleavages that extremely thin lamellae may be split
from them with surfaces that are perfectly smooth. The lamellae are
elastic and in this respect the members of the group are different from
other minerals that possess an almost equally perfect cleavage Some
of the micas are of great economic importance, but most of them have
found little use in the arts
The micas may be divided into four subgroups, (T) the magnesium-
iron micas, (2) the calcium micas, (3) the kthium-iron micas, and (4)
the alkali micas Of the latter there are three subdivisions, (a) the
lithia micas, (£) the potash micas, and (c) the soda micas
All the micas crystallize in the monoclmic system (monoclmic pris-
matic class), in crystals with an orthorhombic or hexagonal habit
In composition the micas are complex The alkali micas are ap-
parently acid orthosihcates of aluminium and an alkali — the potash
mica being KHaAk (8104)3 Other alkali micas are more acid, and
some of the magnesium-iron micas are very complex The members
with the best established compositions are apparently salts of orthosilicic
acid, and, hence, the entire group is placed
with the orthosihcates
All the micas possess also, in addition to
the very noticeable cleavage which yields
the characteristically thin lamellae that are
so well known, other planes of parting
which are well exhibited by the rays of
the percussion figure (Fig, 191) The
largest ra}— known as the characteristic
ray — is always parallel to the chnopinacoid.
In some micas the plane of the optical
axes is the chnopinacoid and m others is
perpendicular thereto In the latter, known
as micas of the first order, the plane of
the axes is perpendicular to the characteristic ray and m the former,
distinguished as micas of the second order, it is parallel to this ray.
The value of the optical angle varies widely In the magnesia micas
it is between o° and 15°, in the calcium micas between 100° and 120°,
and in the other micas between 55° and 75° When the angle becomes
zero the mineral is apparently umaxial But etch figures on all micas
indicate a monoclmic symmetry (compaie Fig 194)
FIG 191 — Percussion Figure
on Basal Plane of Mica
The long ray is parallel to
oo Pob (oio)
ANPIYDROUS ORTHOSILICATES
349
THE MAGNESIUM-IRON MICAS
Biotite ((K H)2(Mg Fe)2(Al Fe)2(Si04)3)
The magnesium-iron micas are usually designated as biotite.
group includes micas of both orders as follows
This
isl Order
Anomite
2d Oraer
Meroocene
Lepidomelane
PUogopiU
The crystals of biotite have an axial ratio 5774 i : 3 2904 with
$= 90° They are usually simple combinations of oP(ooi), oo P ob (oio),
•— |P(ii2) and P(Tn) (Fig 192). Twins are
common, with the twinning plane perpendic-
ular to oP(ooi) The composition face may
be the same as the twinning plane or it may be
193)
witu oP, ooi (c), ooPSb,
oio (6), P, In (ju) and
-JP 112 (<?)
oP(ooi) (Fig 193) The crystals have an
hexagonal habit, the angle IiiAoio being FlG^ ***~^* ^ystel
60° 22!'. The mineral also occurs in flat
scales and in scaly aggregates
The color of biotites varies from yellow,
through green and brown to black Pleochroism is strong in sections
perpendicular to the perfect cleavage, ie, perpendicular to oP(ooi)
The streak of all varieties is white Their hardness =2.5 and density
27-3.1, depending upon composition. The refractive indices for yellow
FIG. 193 — Biotite Twinned about a Plane Perpendicular to oP (ooi), and Parallel
to the Edge Between oP(ooi) and — aP(22i) The composition plane is
oP(ooi) Mica law A=nght hand twin, B and C-left hand twins.
light m a light brown biotite from Vesuvius are' a— 1.5412, /3=i 5745.
They are higher m darker varieties.
Etch figures are produced by the action of hot concentrated sulphuric
acid,
Varieties and their Localities — Anomite is rare. It occurs at Green-
wood Furnace, Orange Co , N» Y., and at Lake Baikal, m Siberia
350 DESCRIPTIVE MINERALOGY
Meroxene is the name given to the common biotite of the 2d order
It occurs m particularly fine crystals in the limestone blocks included
in the lava of Mte Somma, Naples, Italy, at various points in Switzer-
land, Austria and Hungary, and at many other points abroad and in
this country
Lepidomelane is a black meroxene characterized by the presence
in it of large quantities of ferric iron It is essentially a magnesium-free
biotite It occurs in igneous rocks, especially those rich in alkalies
Two of its best known occurrences in the United States are in the nephe-
hne syenite at Litchfield, Maine, and in a pegmatite in the northern part
of Baltimore, Md
Phlogopite, or amber mica, is the nearly pure magnesium biotite
which by most mineralogists is regarded as a distinct mineral, partly
because m nearly all cases it contains fluorine Its color is yellowish
brown, brownish red, brownish yellow, green or white Its luster is
often pearly, and it frequently exhibits astensm in consequence of the
presence of inclusions of acicular crystals of rutile or tourmaline arranged
along the rays of the pressure figure Its axial angle is small, increasing
with increase of iron Its refractive indices are a=i 562, £=i 606,
7=1 606
Phlogopite is especially characteristic of metamorphosed limestones
It occurs abundantly in the metamorphosed limestones around Easton,
Pa , at Edwards, St Lawrence Co , N Y , and at South Burgess,
Ontario, Canada. It is also found as a pyrogenetic mineral in certain
basic igneous rocks,
Typical analyses of the four varieties of biotite follow.
Si02
Ti02
A1203
I
n
HI
IV
40 81
35 79
32 35
39 66
3 5i
tr
56
16 47
13 70
17 47
17 co
2 16
4 04
24 22
27
s 92
17 09
13 II
20
40
I. 2O
FeO
MnO.
CaO i 48
BaO 33 62
MgO 21 08 9 68 89 26 49
Na20 i 55 45 7 oo 60
ANHYDROUS ORTHOSILICATES 351
I II III IV
K20 9 01 8 20 6 40 9 97
H20- \ 90 I , 66
H20+ I219 3*6 I*6' 233
F 10 2 24
(lessO=F) 99 19 99 91 100 83 99 66
I Anomite from Greenwood Furnace, Orange Co , N Y
II Meroxene from granite, Butte, Mont
III Lepidomelane from eleohte syenite Litchfield, Maine
IV Brown phlogopite from Burgess, Can
Before the blowpipe the dark, ferruginous varieties fuse easily to a
black glass, the lighter colored varieties with greater difficulty to a
yellow glass Their powder reactions are strongly alkaline The
minerals are not attacked by HC1 but are decomposed by strong
EfeSO* In the closed tube all varieties give a little water
The biotitcs are distinguished from all other minerals except the other
micas by perfect cleavage and from other micas by their color, solubility
in strong sulphuric acid and pleochroism
The commoner alteration products of biotite are a hydrated biotite,
chlorite (p 428), epidote, sillimamte and magnetite, if the mica is
ferriferous At the same time there is often a separation of quartz
Phlogopite alters to a hydrophlogopite and to penmnite (p. 429), and
talc (p 401)
Syntheses —The biotites are common products of smelting operations.
They have been made by fusing silicates of the proper composition with
sodium and magnesium fluorides
Occurrences and Origin — The biotites are common constituents of
igneous and metamorphic rocks and pegmatite dikes They also are
common alteration products of certain silicates, such as hornblende
and augite They are present m sedimentary rocks principally as the
products of weathering
Uses — Phlogopite is used as an insulator in electrical appliances
and to a less extent for the same purposes as those for which ground
muscovite is employed No "amber mica" is produced in the
United States Most of that used in this country is imported from
Canada.
352 DESCRIPTIVE MINERALOGY
THE CALCIUM MICAS
Margante (Ca(AlO)2(AlOH)2(SiO4)2)
Margante, the calcium mica, is like biotite in the habit of its crys-
tals, which, however, are not so well formed as these Usually the min-
eral occurs in tabular plates with hexagonal outlines but without side
planes It occurs also as scaly aggregates
Analyses of specimens from Gamsville, Ga (I), and Peekslull, N Y
(II), gave
Si02 A1203 FeO MgO CaO Na20 H20 Total
I 31 72 50 03 12 ii 57 2 26 4 88 100 58
II 32 73 46 58 5 12 i oo ii 04 4 49 100 96
The mineral has a pearly luster on its basal planes, and a glassy luster
on other planes Its color is while, yellowish, or gray and its streak
white It is transparent or translucent Its cleavage is not as perfect
as in the other micas, and its cleavage plates are less clastic Its hard-
ness vanes from 3 to over 4 and its density is 3 It is a mica of the
first order
Before the blowpipe it swells, but fuses with great difficulty It
gives water m the closed tube and is attacked by acids
Occurrence — Margante is associated with corundum It is also
present in some chlorite schists In all cases it is of mctamorphic origin
Localities — It occurs in the Zillerthal, Tyiol, at Campo Longo, m
Switzerland, at the emery localities m the Grecian Archipelago, at
the emery mines near Chester, Mass , in schist inclusions in mica
dionte at Peekskill, N Y , with corundum at Village Green, Penn ,
at the Cullakenee Mine, in Clay Co , N. C, and at corundum local-
ities in Georgia, Alabama and Virginia
THE LITHIUM-IRON MICAS
Zinnwaldite ((Li- K- Na)3FeAl(Al(F- OH))2Si5Oi0)
The pnncipal hthmm-iron mica, zmnwaldite, is a very complex
mixture that occurs m several forms so well characterized that they have
received different names All of them contain lithium, iron and fluorine,
but in such different proportions that it has not been possible to ascribe
to them any one generally acceptable formula Some of the most im-
portant of these varieties have compositions corresponding to the fol-
lowing analyses
ANHYDROUS ORTIIOHILK'ATES 353
I IT III IV
Si02. 40 19 59 25 s1 46 45 87
22 79 12 57 l6 22 22 $O
19 78 2 21 66
FeO 93 7 66 ii 6r
MnO 2 02 06 i 75
NasO 7 63 95 42
K20 7 49 5 37 I0 65 10 46
Li20 3 06 g 04 4,83 3 28
F 3 99 7 3^ 7 44 7 94
Total 99 32 102 ii 102 71 105 48
— 0=F= 97 64 99 05 99 60 102 15
I Rabenghmmer from Altenberg Saxony Greenish black with greenish gray
streak Sp gr =3 146-3 IQO
II Polyhlhiomlc from Kangerluarsuk, Greenland White or light green plates
Sp gr =281
III Cryophyllitc from Rrxkporl, Mass, Strongly plewhroic green and brown-
ish led crystals Sp gr « 2 QOQ Contains also 17 MgO and i 06 HgO
IV Zinnwaldile from Zmnwald, Bohemia. Plates, white, yellow or greenish
gray Sp. gr =2 956-2,087 Contains also r;i IIjO and 08
Zinnwalchle occuis m crystals with u,n axial ratio very near that
of biotitc, and a tabular habit Twins arc like those of biotitc with
ooP(iio) the twinning plane
It has a pearly luster, is of many colors, particularly violet, gray,
yellow, brown and dark gieen and is strongly plcochroic. Its streak is
light, Us hardness between 2 and 3 and its density between 2.8 and 3 2.
It is a mica of the second 01 der
Before the blowpipe it fuses to a dark, weakly magnetic bead It is
attacked by acids
Qccumnte and Lotahtic\ — Zmnwaldite is found m certain ore veins,
m granites containing cassiterite, and m pegmatites Its origin is as-
cribed to pneumatolytic processes Us principal occuirences are those
referred to m connection with the analyses
TU& ALKALI MICAS
The alkali micas include those m which the principal metallic con-
stituents besides aluminium are lithium, potassium and sodium. All
these metals are present in each of the recognized varieties of the
alkali micas, but in each variety one of them predominates That in
which lithium is prominent is known as lefodolite; that m which potas-
364 DESCRIPTIVE MINERALOGY
sium is most abundant is muscowte, and that in which sodium is
most prominent is paragomte Muscovite is common Lepidolite is
abundant in a few places Paragomte is rare The first two are im-
portant economically All are micas of the first order, except a few
iepidolites, and all are light colored
Another mica, which is usually regarded as a distinct variety of
muscovite, or, at any rate, as being very closely related to the mineral
is roscoelite In this, about two-thirds of the AlgOs m muscovite is
replaced by VgOj, It is a rare green mica which is utilized as an ore
of vanadium,
Lepidolite ((Li- K-Na)2((Al-Fe)OH)2(SiO,Oa)
Lepidohte occurs almost exclusively as aggregates of thin plates
with hexagonal outlines Crystals are so poorly developed that a satis-
factory axial ratio has not been determined Its variation m composi-
tion is indicated by the analyses of white and purple varieties from
American localities
Si02
A1203
I
II
III
IV
51 52
49 52
5* 12
51 25
25 96
28 So
22 70
25 62
31
40
80
12
undet.
24 ,
OO
20
07
I 34*
°s
02
02
OO
16
13
tr
4 9°
3 87
S 12
4 3*
i 06
13
2 28
T 94
11 01
8 82
10 60
10 65
.
3 73
08
. » *
5 So
S 18
638
7 06
95
i 72
2 Og
i 60
FeO
MnO
MgO
CaO
LiaO
NaaO
KsO
Rb20
CsaO.
F.
BfeO
Total
(lessO=F) 99 45 100 53 99 74 99.63
I. Like-purple granular lepidohte from Rumford, Maine
II White variety from Norway, Maine
III Red-purple variety from Tourmaline Queen Mine, Pala, Cal. Contains
also 04 PjOj
IV. White variety from Pala, Cal
*Mn»08
ANHYDROUS ORTHOSILICATES 355
The mineral is while, rose or light purple, gray or greenish The
rose and purple varieties contain a little manganese The streak
of all lepidolites is white, their luster pearly, their hardness 2 5-4
and density 28-29 The refractive indices of a typical variety are
0=i 5975* 7 ==16047
Lepidohte fuses easily to a white enamel and at the same time colors
the flame red It is difficultly attacked by acids, but after heating is
easily decomposed
Cookeitc fiom Maine and California is probably a weathered lepido-
hte Its analyses concspond to the foimula, Li(Al(OH)2)3(SiOa)2
Occutrencc — The mincial occuis puncipally in pegmatites in which
lubelhte (p 435), and other bi ight-colored tourmalines exist and on
the borders of granite masses and in rocks adjacent to them It is
often zonally mtergrown with muscovitc In all cases it is probably a
pncunutolytic pioduct, or, at least, is produced by the aid of magrnatic
emanations
Localities — The mineral occurs in nearly all districts producing tin,
and also in those producing gem tourmaline Its best known foreign
localities are Jekatcrmbuig, Russia, Rozna, Moravia, Schmttenhofen,
Bohemia, and Penig, Sa\ron> In the United States it is found in large
quantities at Hebron, Pans, and other points in western Maine, m the
tin mines of the southern Black Hills, South Dakota, and in the tourma-
line localities m the neighborhood of Pala, San Diego Co , Cal
Usei> — Lepidohte is utilized to a slight extent m the manufacture of
lithium compounds, which are employed m the preparation of lithia
waters medicinal compounds, salts, used in photography and m the
manufacture of fireworks and stoiage batteries
Muscovite (Ha(K Na)Alj(SiOi)a)
Muscovitc is one of the most common, and at the same time the
most important, of the micas Because of its transparency it is em-
ployed for many purposes for which the darker biotite is not suitable
While predominantly a potash mica, nearly all muscovite contains
some soda, due to the isomorphous mixtuie of the paragomte molecule.
Two typical analyses are quoted below:
Si02 AlsOs FeaOs FeO MnO MgO CaO NaaO KS0 HaO F Total
I 44 39 35 7° * 09 i 07 tr ro 2 41 9 77 5 88 .72 10113
II. 46 54 34 96 i 59 . 32 4* *o 38 5 43 99 63
I. Broad plates of muscovite bordered by lepidoiite, Auburn, Maine.
II Greenish muscovite, Auburn, Maine Total less Q«F n 100.83
356
DESCRIPTIVE MINERALOGY
The crystals are usually tabular and frequently orthorhombic or
hexagonal in habit, though the etch figures on their basal pknes reveal
clearly their monoclimc symmetry (Fig 194) If onentated to corre-
spond with crystals of biotite their a\ial constants are a b c== 5774
i . 3 3128, 0=89° 54', and their principal planes oP(ooi), oo p & (Oio)
|P ob (023), 4P(44i) and -2P(22i) (Fig IQS)
Twins like those of biotite are not uncommon in some localities
Muscovite is colorless or of some light shade of green, yellow or red
It has a glassy luster, a perfect cleavage parallel to the base, a haidness
of 2 and a density of 2 76-3 i Pleochroism is marked in dncctions
perpendicular and parallel to the cleavage, the color of the crystals,
when viewed in the direction perpendicular to the cleavage being lighter
FIG 194
I'll, 1 1)5.
FIG 194 — Etch Figures on oP(ooi) of Muscovite, Exhibiting Monodmu, Symmetry
FIG 195 — Muscovite Crystal with — 2P, 221 (Af)t oP, ooi (<), <wPw, oio (/;),
and 3P«>, 023 (r)
than when viewed parallel to the cleavage The optic al angle is com-
paratively large (56°-76°), in this respect being vciy different from that
of biotite which is small (2°-22°) The mineral is a nonconductor
of electricity at ordinary temperatures and a poor conductor of heat.
Its refractive indices vary somewhat with composition For yellow light
intermediate values are as follows a~ i 5619, j8«- 1.5947, 7= 1,6027,
Before the blowpipe thin flakes of muscovite fuse on their edges to a
gray mass In the dosed tube the mineral yields water which, in some
cases, reacts for fluorine It is insoluble m acids under ordinary coi>
ditions, but is decomposed on fusion with alkaline carbonates.
Muscovite is very stable under surface conditions Its principal
change is into a partially hydrated substance, which may be culled
hydromuscovite. It alters also into scaly chlontic products, into
steatite (p 401), and serpentine (p, 398).
ANHYDROUS ORTHOSILICATES 357
DomounU is a dense fine-grained aggregate of muscovite, often
forming pseudomorphs after other minerals
Senc^te is a yellowish or greenish muscovite that occurs in thin,
curved plates m some schists
Fwhsite is a chromiferous variety of an emerald-green color from
Schwarzenstem, Tyiol
Synthesis — Crystals of muscovite have been made by fusing anda-
lusite with potassium fluo-sihcate and aluminium fluoride
Occurrence — Muscovite occurs in large, ill-defined crystals in peg-
matites, and in smaller flakes in giamtes and othci acid igneous rocks,
in some sandstones and slates and m various schists and other meta-
morphic rocks It is found also in veins It is m some cases an orig-
inal pyrogemc mineral, m other cases a mctamorphic mineral and m
still other cases a sccondaiy mineral resulting from the alteration of
alkaline aluminous silicates
Localities — The mineral occurs m all regions where pegmatites and
acid igneous rocks c\ist It is mined m North Carolina, South Dakota,
New Hampshire, Virginia and other states While phlogopitc (amber
mica) is produced in some countries all the mica produced in this country
is of the muscovite variety
t/iw —Muscovite is used m two forms, (i) as sheet mica, and (2)
as ground mica. The sheet mica comprises thm cleavage plates cut
into shapes It is used in making gas-lamp chimneys, lamp shades, and
windows in stoves. The greater portion is used as insulators m
electrical appliances, though for some forms of electrical apparatus the
amber mica js better Because of the comparatively high cost of large
mica plates, small plates are sometimes built up into larger ones The
ground mica consists of small crystals and the waste from the manu-
facture of sheet mica giound very fine. It is used in the manufacture
of wall paper, heavy lubucants and fancy paints It is also mixed with
shellac and melted into desired forms for electrical insulators
Production — The total value of the mica produced in the United
Stales during 1912 was $355,804, divided as follows. 1,887,201 Ib sheet
mica, valued at $310,254 and 3,512 tons ground mica, valued at $45,550
Of this North Carolina produced 454,653 11), of sheet mica, valued at
$187,501 and 2,347 tons of scrap mica, valued at $29,798, or a total
value for both kinds of mica of $217,299 The imports of sheet mica
during the same year amounted to $502,163, of which 241,124 Ib ,
valued at $155,686 was trimmed and the balance untnmmed The
imports during 1912 were valued at $748,973, and the domestic produc-
tion at $331,896-
358 DESCRIPTIVE MINERALOGY
Roscoelite may be regarded as a muscovite in which a large portion
of the AkOs has been replaced by V20s A specimen from Lotus, Eldo-
rado Co , Cal , gave
Si02 Ti02 A1203 V203 FeO MgO K80 H,0- H,0+ Total
45 17 78 ii 54 24 01 i 60 i 64 10 37 40 4 29 99 80
besides traces of Li20 and Na20
The mineral occurs as clove-brown or green scales with a specific
gravity of 2 92-2 94 It is translucent and has a pearly luster and a
strong pleochroism. Its refiactive indices for sodium light are, <x= 1,610,
0=1685,7=1 704
Before the blowpipe it fuses to a black glass. It gives the usual
reactions for vanadium m the beads and is only slightly alTccted by
acids It has been found associated with gold m small veins ncui Lotus,
Eldorado Co., California, in seams composed of roscochte and quartz
between the beds of a sandstone in the high plateau region of south-
western Colorado, and as a cement of minute scales between the grams
of the sandstone on both sides of the seams. In all cases it appears to
have been deposited by percolating water, possibly of magmatic origin
The impregnated sandstone is mined as a source of vanadium The
material, which contains an average of about 3 per cent of metallic
vanadium is concentrated by chemical processes, and the concentrates
are manufactured into ferro-vanadium. Most of the vanadium pro-
duced in the United States is made from this ore,
Paragonite ^(Na-KJAlsCSiO-Oa)
Paragonite, the sodium mica, differs from muscovite mainly in com-
position Both contain sodium and potassium but in puragomte the
sodium molecule is in excess
The analysis quoted below is made on a sample from Monte Cam-
pione, in Switzerland
Si02 AI203 Fe203 Na20 K20 H20 Total
47 75 40 10 tr. 6 04 i 12 4 58 99 59
It occurs in the same associations as some forms of muscovite but it
is much less common. It apparently occurs most abundantly in certain
fine-grained mica schists to which the name paragonite schists has been
given, It i§ m ail known cases a product of dynamic metamorphism*
CHAPTER XVII
THE SILICATES-Cowfowwrf
THE ANHYDROUS METASILICATES
NORMAL METASILICATES
Beryl (BeaAl2(Si03)o)
BFRYL is a frequent constituent of coarse-grained granites. It is
important as a gem matciial, and is particularly interesting because of
the many physical investigations that have been made with the aid of its
crystals
Although the mineral is essentially a beryllium alummo-rnetasilicate,
it usually contains also a little FesOa and MgO, in many cases small
quantities of the alkalies, and in some cases also caesium. Analyses of
a green beryl from North Carolina, an aquamarine from Stoneham, Me ,
and a light-colored crystal from Hebron are given below
Si02 AfcOi Fe20;j BeO FeO Na20 Li20 Cs20 H20 Total
I. 66 84 19 05 . 14 n . ....... 100 oo
II. 66 28 18 60 . 13 61 ,22 ,, ,. .83 90 54
III 65 54 17 75 21 13 73 71 ... 2 01 100 39
IV, 62 44 17,74 40 ii 36 ,38 i 13 I 60 3.60 2.03 100 30
I Theoretical
II, Alexander Co,, N. C,
II I Stoneham* Me.; ako.o6%CaO.
IV, Hebron, Me
The mineral occurs massive without distinct crystal form and also in
granular and columnar aggregates, but its usual method of occurrence is
in sharp and, in some cases, very large columnar crystals with a distinct
hexagonal habit (dihexagonal bipyramidal class), and an axial ratio
i : 4989. The forms found on nearly all crystals are oo P(tolo),
ooP2(ii2o), oP(oooi), P(ion), P2(ii22) and 2P2(ii2i) (Fig 196),
In addition, there are present on many crystals other prismatic forms
and the pyramids 3?f (2131) and aP(ao3i). Other crystals are highly
359
360
DESCRIPTIVE MINERALOGY
modified (Fig 197), the total number of forms that have been identified
approximating 50 The angle icli Aoi7i = 28° 55' Some crystals
are very large, measuring 2 to 4 feet in length and i ft in diameter
Beryl has a glassy luster It is transparent or translucent It is
colorless or of some light shade of green, red, or blue Its streak is
white, hardness 7-8 and density 2 6-2 8 Its cleavage is very imperfect
but there is frequently a parting parallel to the base Pleochroism is
noticeable in green and blue crystals Its refractive indices for yellow
light at 20° are co= i 5740, e= i 5690 They become greater with increas-
ing temperature
Before the blowpipe colorless varieties become milky, but others are
FIG tg6 1'ic, 197
FIG 196— Beryl Crystals with °op, ioTo (w), oP oooi (c), <» P2, 1120 (a), P,
loii (p) and 2?2, 1 121 00
FIG 197 — Beryl Crystal with m, c, p and A as m Fig 196 Also 2p, 202 1 (M) and
3Pg, 2131 M
unchanged except at very high temperatures when sharp edges arc fused
to a porous glass The mineral is not attacked by acids.
Beryl is distinguished from apatite, which it much resembles, by its
greater hardness
It alters to mica and kaolin (p 404)
Syntheses — Beryl crystals have been formed by long heating of
8162, AkOs and BeO m a melt of the molybdate or vanadate of lithium,
and by precipitating a solution of beryllium and aluminium sulphates
with sodium silicate and heating the dried precipitate with boric acid
in a porcelain oven
Occurrence —The mineral occurs as an accessory constituent m peg-
matites and granites, in crystalline schists, especially mica schists and
ANHYDROUS METASILICATES 361
gneisses, m ore veins and sometimes in clay slates and bituminous lime-
stones
Uses — The transparent varieties are utilized as gems, under t 
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